Windows 8 Live Tile sizes

I've been playing with Metro development lately, and I've noticed a peculiar property of the Live Tiles where they're not displayed at the same size on every screen.

Tile graphics are defined by the developer at 150x150 pixels. Using the 10" 1366x768 screen on my tablet, that's exactly the size they're displayed at. If I connect the tablet to an external 24" 1920x1080 monitor, however, every tile is scaled down to 120x120 pixels. I originally noticed this because it causes some of the app titles to wrap to two lines even though they were a single line on the tablet's screen.

This behavior strikes me as very odd. Why would the system need to make the tiles smaller on a screen that's significantly larger and would have plenty of room to show quite a few of the full-size tiles?

I couldn't find any documentation from Microsoft about why this is done, but I did a little investigating with the tablet simulator that's included in the SDK and it looks like the full-size 150x150 tiles are exclusively used on 16x9 10" displays. For example, a 10" 16x9 display running the exact same 1920x1080 resolution as my external monitor will use the full 150x150 tile (scaled up for pixel density, of course), but a 10" 4:3 display running at 1024x768 will use the smaller tiles as will every 12+" display regardless of pixel density or aspect ratio.

This isn't really a big deal, it's just strange. It's obviously intentional behavior designed by Microsoft but I can't come up with any logical explanation for why they did it that way. Anybody have any theories?