Its pretty much 3 things:
1. the general shock of people when I tell them my set-up
2. the fact that I'm always looking at bikes (its just what I do)...and most bikes I look at don't seem to have enough seattube length in them to enable to me to actually ride them (with a 900mm saddle height)...I'm 6'5" not 7 foot!
3. when you look at bike radar and have a look at the riders' heights combined with their saddle heights mine just seems way off. Like Tom Boonen (6'4" - saddle height of 820mm) or George Hincapie (6'3" & 800mm). Even after accounting for long legs/short torsos/long femurs, etc...

So I guess I'd ultimately like to be able to have a saddle height that is transferable to any (XXL) bike...cos at the moment there aren't many bikes with seattubes long enough to accommodate my 900mm saddle height without the use of a 400mm setapost and a 17+cm seat to bar drop (both of which are not ideal)