... First thing I did was to have a read of wiki's entry for IE10; according to them, there were in total six IE10 Platform Previews released; the first two ran on Win7+, but the last four ran only on Win8.
Did your successful test involve IE10 Platform Preview 1 ? It appears that "the first preview release came four weeks after the final release of Internet Explorer 9", so it might be that the code hadn't diverged much then from IE9 Final, hence your ability to run it on Vista...
I managed to grab myself a copy of iepreview.msi file, with a digital signature of 2011-11-22 (probably Platform Preview 2), but am reluctant to run it on my main Vista SP2 laptop; what impact, if any, did it have running on your system? Running just the extracted iepreview.exe (hence in semi-portable mode), how was the (installed) version of IE9 affected? ... and what about file associations and the like?
Intriguing as your experiment seems, I think it's just that - an experiment; this IE10PP(1?) can't be used as a permanent replacement to IE9, plus it won't receive any security updates from MS; while, OTOH, IE9, with all its inherent flaws, will be patched until Jan 2020...
BTW, have you tried running the .msi directly? I did myself; it doesn't warn me of an incompatible OS, in fact it appears as though the installation will proceed once I accept ToS:
I haven't though, and cancelled the installation...
OTOH, trying to run IE10-Windows6.1-x86-en-us.exe (off-line installer for Released IE10 for Win7) alerts me to the fact that:
On a later date, when I'm feeling more adventurous, I might create a Restore Point and then go on with the ie10pp installation, just for the sake of it...