Dual-display DVI KVM switch box question

I was just looking for a switch-box solution so that two computers -
both with dual-DVI-display - could share the same pair of monitors.
We're Purchasing a new comp that will mostly be used as a server - but
want to be able to use it as nice display box from time to time. We
already have plenty of dual-head systems with monitors but no more
space for an another 2 heads. So, I'd like to use a switch box so
that the two systems can share the same keyboard/video/mouse. That
seems straightforward enough

What surprises me is that DVI,USB KVM switch-box for a dual-display
system is more than 3x the price of what is apparently the same switch
box for a single-head system. I thought it should be less than 2x the
price - because couldn't I essentially get the same functionality with
2 single-head switch boxes (except that I'd have to press two
buttons).

Am I missing something or is there such a steep premium for
convenience?

The ones I was looking at are from Gefen:

($199) single head: http://www.gefen.com/kvm/dproduct.jsp?prod_id=3113
($649) dual head: http://www.gefen.com/kvm/dproduct.jsp?prod_id=4178

Looking at the tech-specs, I can't see a difference.

Thanks.

-JJ