I am pretty sure they do access more than 2 gigs of memory.
If you do a search, you can find more info, posted a month or 3 ago, about this very subject. This is perhaps the reason why none of the gurus here have not chimed in ( as this has been discussed lately )
Now, you also have to remember this, - if your app is using 2 gigs of memory, and you only have 2 gigs available, then what is your OS using to stay up and running. your app is not using a full 2 gigs in reality, and so, with that said, more than 2 is better, so the app can use that full 2 gigs of memory, and an extra 2 for your OS of choice to use to stay up and running.