Well, fact also is that an i7 from HP costs $1460 (list price) whereas a MacPro costs $3300 (list price). I haven't seen any comparative benchmarks but I doubt that the performance of the mac pro is more than double the one of HP. Has anyone seen a benchmark?
Of course, HP is just an example, there are other hardware makers who offer similar stuff. That's another advantage of PC: there's competition between hardware producers, whereas Apple is alone doing their machines.

And until now I still haven't seen my list of arguments being defeated... :-)

Regarding consumer base, because it's so small, it's only natural that it grows. Any smaller and Apple would disappear... ;-)