With the latest release of the patching tools you can easily patch just about anything. I've patched PlayTV 2.03 as its 3.56 firmware and I just patched NFS Most Wanted 1.02 update as its only an eboot and it works.
The reason I added the param.sfo into the patches is to change the firmware version from 4.xx to 3.55. Its not needed, only the eboot.bin is needed to patch it so it shouldn't matter which version you got US or EU, just use the eboot.
I have many games and only 1 patch, I just copy the eboot over and it still runs. There are only a handful of games that are actually region specific, like if its censored in a region it might need a different eboot but if every region has the same game then the same patch will work.
not sure? There are a few games with extras between the EU and US versions. Mortal Kombat has extra movies same as Gran Turismo 5 also has extra movies making them bigger than the EU versions.
Maybe the US version has more languages like Spanish where the EU version might be English only?