The Epic is missing the 16gb internal SD card... the SD card that Samsung has split into 2GB for apps and 14GB for /sdcard for the rest of the US Galaxy S devices (no idea how the EU phones are set up). As a result, it has far less space for apps, but it more than makes up for it in speed.
About the only thing that I think Samsung can do to improve speed on the rest of the Galaxy S phones is to either work like hell to come up with a better driver for the internal SD card, or to accept a massive limitation in app space and build in the original lag fix.
I'm hoping it's just a driver issue... when copying a 1GB file to and from my /sdcard using the USB mass storage mode, I sometimes see 10+ megs per second, and sometimes see >1 meg per second. This is with my phone sitting idle, nothing else going on at all (except for OS Monitor, so I can see what's going on). That leads me to believe that it's either a driver problem or the internal SD card is the world's crappiest. Seeing as everything else on the phone is very nice hardware, and seeing how the GPS and compass drivers have issues as well, I'm kinda (and maybe foolishly) thinking that it's probably a driver issue. We'll see.