So this is interesting. I've been using the Windows 8 Consumer Preview since Monday on a Samsung Series 7 tablet, as you may know, but since yesterday have been loading it on the various PCs I use regularly. And one difference has stood out.
In this case, a picture really is worth a thousand words. So here are two:
First, the Windows 8 Start screen on the Samsung tablet:
Now, the Windows 8 Start screen on the Lenovo ThinkPad 420S:
See the difference? The tablet version offers three rows of tiles, while the laptop version has four. Here's the thing: they both have exactly the same screen resolution, 1366 x 768. And, yes, the DPI settings are the same for both. So why would the tablet show less?
My theory is that this is related to touch, that because the table exposes touch capabilities, Windows 8 scales up the user interface to make bigger touch targets. But I really don't know.
Update: A number of comments below wonder about the screen size differences between the two devices, and this seems like a reasonable avenue for finding the answer. The Samsung tablet has an ~11 inch screen, while the ThinkPad T420S has a much bigger 14-inch screen. So that could indeed account for the layout differences seen here. That or the touch capabilities, or a combination of the both. Interesting that Microsoft might be looking at more than just the resolution either way.