Cache folder worked exactly the same way in ut2k4, I dont see that as a valid reason. The friends thing is/was annoying but hey, most of us are on steam now anyway.
No, zunnie has it right. The map sizes in UT2K4 were typically much much smaller. You can only fit a handful of UT3 maps in the default 300 Mb cache. So, you are downloading the same stuff over and over. The largest maps are WAR and vCTF, many are >100Mb each in size. DM and CTG are usually smaller, but still larger than the UT2K4 variety.
So what if you increase your cache size to 200 Gb? That works fine until your ini file gets overwritten by the default and you cache gets erased before you can replace the ini file with your backup.
I doubt most players are on steam, I am not and none in my clan are that I am aware of. So details like playing musical friend invites may turn off some players.
The game had an awful rough start and just never recovered. Video card drivers were a huge problem for many vista users as well as many xp users with high end or newer cards. ATI and nvidia did a really poor job for the first 6-9 months after the game was released. If you cannot run the game due to crashes for a long time, well I guess you just give up. I know of many who walked away early due to incompatible hardware. That is also part epics fault for not testing the game properly before release and not pressuring ATI and nvidia to fix the drivers.