Wind your neck in sunshine, I asked a very valid question. You're suggesting that every server support engineer this side of a worthwhile qualification is wrong - if you were a chippy who goes to the pub with a guy who knows someone with an IT shop... You get the picture.
The fact is that yes, 64-bit Windows can see and use 8GB, and yes, there is a marginal performance difference. However, the guy at home watching p**n, downloading music and writing his CV will not notice, and that is the point.
Hell, in the server world only larger applications are run on 64-bit OS's, rather than 'just cos it can and it's got 4GB' - SQL, large numbers of IIS sites, Oracle, yes - all run on 64-bit with shitloads of memory. A domain controller, Exchange 2003, reverse proxy, all run on 32-bit because there is NO reason whatsoever in running it.
As you say, very little point continuing with the discussion as he is currently running 64-bit Windows. Have a good evening and smile - it might never happen