Actually, by walking distance the St. Regis is NOT closer than the Fairmont to Kerry Center--actually, it may be about 10 minutes LONGER. By taxi it would be easier than Fairmont, though, since it is on same side of Jianguomen Blvd. Walking from the Fairmont you would use the pedestrian underpasses beneath Jianguomen to get to the north (Kerry) side--I agree with moondog--20 minutes' walk is about right from Fairmont-Kerry.

That said, I recommend you look into the Grand Millenium Hotel, which is not quite 1 year old, and an easy 5 minute walk south to Kerry Center so no taxis needed. Also right next to a subway stop. Friends of mine who used to live in Beijing just came back for a visit and stayed there for convenience--his office is next to Kerry Center. They had very good things to say about it. You might also check out the new Fraser Suites CBD--they are serviced apts but will do short term deals. Also only 5 minute walk to Kerry. I live just up the street from Kerry and these two options are the closest thing other than Kerry Hotel itself. Next closest after that are Traders Hotel, China World Hotel and Jinglun Hotel, walking distances range 10-15 minutes, CW being the most upmarket and often full.

I would caution you on curbing your expectations in a completely new hotel (like the Fairmont)--hotel service in China, even at name-brands--is often quite uneven in the first several months after a hotel opens while proper staff has to be located and trained. To your last question...the area around the Fairmont is not "new" but has undergone heavy re-development. Regardless of where you stay, there will be plenty of places to eat, shop, etc. nearby.