I could be wrong here, but it seems that another benefit to polymer guns is that they're easier to make more comfortable. Most manufacturers seem to have figured out how to mold an extremely comfortable grip out of polymer - HK p30, Walther PPQ, S&W M&P etc..
Now that I think about it though, that may have more to do with how new the designs are from both companies than with the frame material. With the exception of a few pocket pistols, it doesn't seem like there's been a lot of innovation in metal framed guns in recent years.
si vis pacem para bellum