Some of this stuff is a bit dubious for discussion here.
However there has only ever been a Series 1 Tivo sold in Europe (so far) - which has suitable electronics to capture UK (aka 576/50i PAL Composite and RGB) TV signals (and with a PAL I NICAM tuner for analogue broadcast TV). The Series 2 and Series 3 models sold in the US are NTSC/ATSC only - though I'm not sure about the Australian models which I assume are DVB-T compatible.
In Aus there were some US S1 models converted to PAL (prior to their launch in Europe) - though I think the S2 and S3 are significantly more "locked down"? (In fact I think the original network card design was courtesy of an Aus Tivo owner who is also behind the Linux Samba stuff? )
Given that all users currently with Tivos in the UK (with few exceptions) are likely to have Thomson Series 1 boxes, then it makes sense to target these for upgrades, rather than expecting people to source a new Tivo as well?
As for the hard drive replacement - it's the easiest way to upgrade a Tivo for users who don't have network cards, or aren't PC tinkerers and happy with connecting hard drives to their PCs etc. It is just a straight swap out for the existing hard drive - much easier and significantly more robust.
I upgraded my S1 Thomson UK Tivo to TivoWeb, Mode 0, Ethernet listings update etc. with no major hassles, but I'm pretty PC literate and build my own computers.
I suspect that any "roll your own" EPG upgrade will also be possible without a hard drive swap if you've already got Telnet etc. access to your Tivo via the network.
