They went for a battery life and got it
I have always been impressed with the battery life of Apple notebooks (and all of their portables). From the first iBooks I get about 5 hours under normal use and 2 hours under heavy use (full out CPU plus spinning optical drive). That blows away the PC competition where I'm lucky to get 2 hours under the best of conditions. As I use my laptop on train commutes and flights this battery time is important to me.
Since 2003 they have delivered on their near 6 hour promise as I usually get around 5. That's well adequate for a train commute (unless you are really unlucky) or a flight across the US. But now with this enhancement, dropping the CPU to 2.4 GHz and improving the battery I couldn't resist trying the latest model with the 10 hour claim. And Apple did it. When I untether I get about a 9 1/2 to 10 1/2 hour life with normal use or 3-4 hours under heavy use. That's outstanding. I can use my Pro for about as long as an iPad.
Another thing that impresses me about the latest Pro 13 inch models is they dissipate heat well. They do get hot, being smallish laptops, but feel less hot than my polycarb 13. I am guessing that is because the aluminum unibody conducts heat better than plastic. I find the polycarb actually uncomfortable after a few minutes (and buffer the heat with a pillow) but can use the Pro on my lap for hours.
The computer is a joy to use. It continues to have all the plusses of OS X and Apple's fine aesthetics. As the product has been reviewed so well for all around use I just wanted to give it 5 stars for my positive experience of no complaints. I use these laptops for my livelihood and they are running for ten to sixteen hours every day with no glitches. Plus Apple's agenda to give an outstanding battery life to the latest generation is a total success in my opinion.
NOTE: As a followup I have bought three of these computers this year and returned one because of quality issues. From my (and others') experience with Apple I think my problem was just bad luck, but worth mentioning. So this year I bought two flawless MacBook Pro 13's and one that had the following issues. First I noticed excessive "head parking". I know the Pro's have an aggressive head parking algorithm and you often hear the loud click. But one day I had mine totally stationary on my desk in clamshell mode (mounted in an arc) and it just kept clicking away. The OS seemed fine otherwise and it just happened one day. After that I noticed an odd click now and then in clamshell mode. Second, and what got me to return this machine, is that within two weeks the "K"-key got stuck. It still worked, but was tweaked enough that my moderately good typing was no longer possible. So, as I was still within Amazon's return period, I returned the machine. That said I have two other MacBook Pro 13's this year and I have been totally satisfied with them. No other quality issues.