Loads WAY different JS resources:

Mobile: http://www.webpagetest.org/result/130105_QH_4GR/1/details/

IE10: http://www.webpagetest.org/result/130105_WY_4H7/1/details/

It's the same /URI/, not the same code behind the scenes. What you seem to be suggesting is analogous to saying that because two businesses share the same physical building, they're the same business (think skyscrapers).

EDIT: While I don't work for Google, I bet it's not even the same team that works on the mobile maps site vs. the desktop maps site.

Why not? It's obviously not the same codebase as the desktop version of the site, why would you expect because the desktop version of the site supports IE10 that the mobile version of the site would as well?