Jay,
It might have to do with the resolution that laptop is set too, the Acer you listed has a 1600x900 screen while the other one is only running at 1366x768 because its the 15" version of the same laptop, there it is easier to run higher details... you could run 1280x720 on the Acer though and get better frame rates...
If and WHEN I get another 17" Acer it will be the Acer Aspire V3-771G, but I KNOW that I've seen them with the Nvidia 650M for around $800 and I know that its better than the 640M so you might see if you can find a model with that GPU.
The 650M should be able to run games on high settings with the 720p resolution. Ultra is a stretch though... I don't think a GTX660M would run the game on Ultra, because its based on the desktop 640 core (GK107), and the desktop 640 core struggles on Ultra.
I edited this post to link to the Skyrim benchmark for the GK107, the laptop GPU's performance would probably be a 'little less' than what's listed here:
http/www.tomshardware.com/reviews/geforce-gt-640-review,3214-4.html
Skyrim is also a CPU dependent game, so in theory, Skyrim should run better on it, but the difference might be something like 2-5 fps at such low resolution.
Dry