I think he's referring to the fact that you can only install apps on the device not the SD card (until froyo or until rooting) and that the device has limited space for this (378 MB) similar to the Pre's original space restriction with partitions.
While I agree that this is a somewhat silly restriction, it's not anywhere near as big of a problem as it was on the pre. A good way to check if it'll be a problem for you is this site:
AppBrain - the best Android apps and games on the Android market
Not only is it a good site in that you can queue up apps to be automatically installed on your phone later, but it gives you information about all the apps you've selected. I've chosen 85 apps that I'm interested in and I am having trouble finding more beyond that. Thanks to appbrain I know that only 11 of those are not free and their total cost is $31.70 (I may chose not to get a few of them) but also that all 85 together use only 107 MB. That's less than 1/3 of what's available on the EVO.
Android apps are teeny tiny. Even the big 3D games from Glu and all those other publishers. What they do is keep all their
data on the SD card and only a very small executable on the actual device.
Cheers!