One thing I have noticed about Cisco wireless cards is that they have better gain than other vendor cards. Cisco card has inherent LEAP support which means you dont need a supplicant to run LEAP, like you do need on other vendor cards. Ofcourse you could use EAP, but then if you dont have Windows XP, you dont have inherent support for EAP on other operating systems.
If you look at the other vendor wireless products versus a cisco wireless product, its not just a few common standard features like WPA that is supported by Cisco. Cisco bundles tons of features which are not really available from most vendors.
Of course 1200 is modular compared to 1100. 1200 can be upgraded to 802.11a or 802.11g type. You can have 802.11a and 802.11b running at the same time too. Obviously the difference in pricing. PEAP is supported in both the access points. Infact the capability to do PEAP infact depends on the software that you load on the AP.
Sankar Nair
UC Solutions Architect
Pacific Northwest | CDW
CCIE Collaboration #17135 Emeritus