This thread seemed to have died out, but I just now got time to put my thoughts down on paper. This contains many of the elements already discussed.
This is a case where the approach is itself a potential trap for the pilot. Our point in analyzing accidents should be to learn from them, not to condemn the victims and all prior posts in this thread appear, commendably, to share this view. To my view this is more than a simple failure to identify a navaid, but rather a complex series of conditions which led to the apparent fatal failure to properly tune and identify. To understand this series of events I think we need to first understand what components an ideal ILS approach would have and understand how the lack of at least one of those components might have contributed to this accident.
But, before I go there note that the bottom line will be this - and you don't need to read any further. Always, always, always place the approach aid in the primary nav display at the time you brief the approach and don't take it out until you go missed (and even then you probably will leave it in for the next attempt).
One of my all time favorite ILS approaches is ILS 24 at Nantucket, MA because it is in my opinion a perfect ILS approach. You can find it here:
http://204.108.4.16/d-tpp/0503/00659I24.PDF
Let's take a quick look at it to see why I think so highly of it. First, it is a full ILS which does not require radar to execute it. It has a Holding patterns in lieu of Procedure but that's okay its just another method of getting the job done. Second, it has a compass locator Third it has DME associated with Localizer (this is the first component on this approach that I would give up) and fourth, it has a good approach light system.
Okay, for comparison the ILS 4 at Hobby:
http://204.108.4.16/d-tpp/0503/00198I4.PDF
This is basically just a GS and a LOC to a runway, with DME on the LOC. What it is missing is any method to execute it on your own because it has no way to know where you are relative to the LOC course or along the LOC course if you don't have DME, and so RADAR and DME are required, it has an okay approach light system.
From the pilot's perspective the Hobby approach is much more complicated, it may look easier, but it is not.
Let's start by flying the ILS 24 at ACK. Setting up the approach we dial in WAIVS in the ADF and once identified we now have a reference to our lateral position relative to the OM - in other words you have situational awareness - you know when the LOC is going to come alive. It is a LOM so it is good for 15NM miles, which is quite adequate for ILS approaches. We set up our number one VHF NAV receiver to receive the LOC frequency, and that is all that is required to shoot this approach, now a prudent pilot would also set up the ACK VOR in anticipation of the missed, and technique could vary (is it in the standby for the number one or is it in the primary for the number two? There are any number of reasonable variations.) The key here is that with the LOC/DME and the LOM we always know where we are and we need NOTHING else to know this. In fact, if we just had a LOC (no DME) the LOM would give us enough information to comfortably fly this approach without looking to other navaids for valuable information. Though I would want the DME off of the ACK VOR, but that is nice to know, not need to know.
Now let's fly the HOU ILS 4 approach. Well our first problem (assuming we do not have a moving map of some sort, which I'll assume) is how do we know where we are? There is no LOM, but there is LOC/DME. So if we dial the LOC in the number one, we know our distance from the departure end of the runway and not much else. So now we need to find another navaid to tell us where we are laterally. The HUB VOR will do, not perfect, but close enough. Should we put the HUB in the number 1 and then when we get on the LOC switch to the LOC frequency? What course do we dial in? - why the LOC course since the HUB VOR is close enough. Well that works, but now we need to know when the LOC is alive so #2 needs to be tuned to LOC. When the LOC comes alive we need to switch number one to the LOC and either leave number two on the LOC as a back up, or set it up for the missed. This is really a trap for the unwary when things get busy or you simply are distracted by the radio. You can easily miss the fact that you are still tuned the VOR as your will basically have a proper looking intercept going.
Of course we could set the number 1 to the LOC (tune and identify) and the number 2 to the HUB VOR (tune and identify) and then we have it properly set. If you fly single pilot IFR in a light aircraft this is probably the strategy you would employ. However, in two pilot transport category aircraft it is likely that the CA and FO have HSI displays for number 1 on the CA side and number 2 on the FO side, but do not have a second omni head. What they do have is an RMI on each side. So if the CA wants to maintain situational awareness without falling into the trap of having the HUB VOR displayed on the HSI, then s/he needs to tell the FO to set the HUB VOR on the number two (depriving him/her of the LOC on their HSI) and use the RMI for reference. This is the best you can do in this situation.
So this is where I end up: Always, always, always place the approach aid in the primary nav display at the time you brief the approach and don't take it out until you go missed (and even then you probably will leave it in for the next attempt).