You make it sound like a 1.5kW PSU draws 1.5kW all the time, but it only draws what it needs. (if the computer only needs 200W, it will draw 200W from the PSU). However, having an oversized PSU and running it on an underspecced PC might make efficiency suffer, that is one truth.

And yes, 1.5+ kW PSUs are rarely needed, except for those people would would be nuts enough to run dual quad core Xeons and 4 x GTX295 cards. Which are probably in the vast minority even among enthustiasts.