I'm not arguing against that. For myself, I'd pick the 650's over the 900's any day (though I'd probably take the T50rp's first). I'm talking about someone that is new to high-end audio that as far as I can tell, is a basshead. Yes, the 650 is better, but isn't the signature or the design (open/closed) that he's looking for. I wouldn't say the 650's are bass light, but I'm sure he very well may if he heard them. Usually people in this position are looking for headphones like the XB500, HFI-580, etc, which have lotsa bass.
Recommending a 650 for a newbie basshead is like recommending a Lotus for someone who only cares about the 0-60 time. Yes, the Lotus is overall the better car, it can handle, turn, it's nimble and fast. But, that person would be better suited to a big V8 car because all he wants is acceleration.
Point taken, it's up to him really.