Compression is a key factor.
Also even though blu ray has a larger capacity there are sometimes problems reading data. Blu ray is also notoriously hard to develop for hence why console versions of multiple platform games are usually developed for 360 and ported to ps3.
I am in no way saying that 360 is superior but it does have a much larger fan base than the ps3 due to various factors. Money being the main one and in this day and age who can blame a gamer for being careful with their money. Why pay £300 for something you can get a similar product for £180 that does the same job and just doesn't have a blu ray player you probably don't want anyway!
As for pc there are problems there too one being cost! To keep a machine to decent gaming standards can cost anywhere between £50/£100 per year just to keep up with th latest tech to be able to run every game at 100% plus quality.
I am not saying the 360 is the superior choice it also has problems, 360 freezing/overheating etc etc but it is the most popular of all gaming platforms bar maybe the ds or wii and quite frankly if they released TES:Wii then I wouldn't give up gaming for good.
On a side note however I love PC gaming and do feel for a lot of things it is the better choice for me anyway and as soon as I can I will be getting a new machine. I also plan on getting a ps3 this month as well, I am a pure blood gamer and have owned every console since the NES and Ben have a collection before that so I know a little bit about gaming