It's david clapp.
Take a look at the gallery Small World. The 2nd, 4th, 12th photos all have this blur. Either it's done through PS or maybe it's the effect of the lens
i see, marc adamus has shared his condensation technique in another site before, he is a person who is very willing to share, so i thought you were talking about that.
ah, i see the photographs that you talk about. this effect can be achieved by
tilt shift lens use, here in clubsnap giantcanopy and Leong23 are two people who use TS lens extensively, you can look at Leong23's APAD
here or giantcanopy's Singapore series
here to see more.
anyways, i am not sure if david clapp uses a TS lens or not, i am not really a fan of such, but it can also be achieved artificially (albeit with different feel and result, if you ask me) with photoshop. this is called the toy train effect,
here got one big big thread on it..
receding hairline has a tutorial on how to do this in photoshop
here.