Whats the problem with the Ikelite housing? Has anyone ever used one with this camera? I just can't understand how someone would pay 4-5 times as much if there is something available that works, unless there are certain advantages to using the nicer housings that I don't know about.
Sort of a loaded question in general about why get other housings when less expensive ones are available, but you can ask the same thing why would someone want a Porsche instead of another car, they both get you from Point A to Point B
And of course people will vary in opinions.
I do not have that camera/housing combination, but housings are different in terms of the material used to build them, how controls are designed and laid out, general ergonomics, depth ratings, ability to add accessories/change lenses and many other factors. It is not just the housing you are looking at but pretty much for every still and video camera out there.
Many people use Ikelite, but many people also use the other housings also because they have the features they prefer. For instance I much prefer aluminium/metal housings myself.
In general you want a housing that allows you to access certain controls in a housing. If you poke through the video forum you can find many discussions about what features are desired (and whether people prefer manual or electronics housings.)
Some basic features you should look for as a start (and many housings have them) are Manual Focus and Manual White Balance access.
Which other housings were you looking at? Take a look at the specs for those housings and you can see if there are any differences that are important to you (or ask if the things are important to have back here, I am sure people will jump in with thoughts.)