I just bought a new MBP at the same time that these came out and I couldn't think of a single reason other than "it's shiny" to even consider getting the new MacBook. The 13" MBP is still plenty light, but is a lot more powerful.
My general understanding is that purses are kind of informally and loosely divided into:
Clutches, which are the size of a large woman's wallet -- or a small woman's wallet for that matter. They basically can hold your keys, a credit card, your phone, and maybe some lipstick, and that's about it. Women carry clutches in places where style is more important than functionality, and they go with, like, cocktail dresses and such.
Generic purses, which are maybe twice to three times the size of a clutch, and generally speaking a woman can comfortably put her wallet in there, enough make-up to handle at least an ordinary day in the office, her keys, her phone, and then at least a small amount of additional miscellany. My wife's larger purses will hold a netbook but not a notebook computer.
Totes or messengers, which are typically larger than a normal purse, and might plausibly carry a standard-sized laptop. (My wife, who is small, doesn't carry any purses this size -- she'll use a cloth shopping bag if she needs to carry things this size). My sense is that they are regarded as less fashionable. You might see them referred to as "mom bags," since mothers with small children often carry larger purses than usual.
Doing a bit of research for this post, I have discovered that descriptors that I thought were purely about size are also to do with other factors such as whether the purse has internal subdivisions and/or its strap or shape styles. So some people might use these terms differently.