Original EVO had less than 1GB, EVO 3D has 1GB reserved for apps I think and it's pretty darn hard to fill unless you insist on installing dozens of large games to phone memory (from what I've seen, a good majority of games these days install to SD automatically or download their data there).
HTC did the dual partition formatting in order to enable standard USB mass storage mounting to PCs, which imo is a LOT more convenient than the MTP protocol tablets and Nexus/stock ICS devices use to transfer stuff to the phone. The downside is split partitions obviously, and the phone not being able to access the extra 10GB or the removable card while connected to a computer.
I believe Samsung's doing the same thing... Personally I think it's a valid compromise, MTP is a kludge and won't transfer half the stuff I feed it, plus it doesn't let you use the phone as a data drive.