I don't see the battery being a problem. I rarely see people with extra batteries any more. I stopped carrying an extra battery about 8 years ago. I now use a 17" MBP. Nearly any place I go I can get an AC adapter. Every meeting I go to the first thing everyone does is start looking for adapters. At conferences they generally bring out extension cords so everyone can use their adapters. Panera Bread has adapters all over the place. Most airports are starting to provide better access to adapters.
The need for a second battery is clearly fading. If you really do need longer battery life I think there will be third party, external solutions. Even if Apple doesn't open up the Magsafe connector design Xantrex and others make portable inverters with rechargeable batteries so that you can simply plug in your AC adapter and get extended power that way. No big deal.
On the plus side, if the battery is built in it makes the notebook case stronger as it doesn't have to have a hole in it. It means the battery is cheaper, smaller and lighter as it doesn't have to have its own case and connectors and built in electronics. Currently the battery shell has the same design as the notebook which surely adds to the cost.
Are you freaking kidding? Most airports are "starting to provide better access to adapters"? You obviously haven't spent much time in, oh, I don't know, JFK, or LAX, or half a dozen other airports I can think of offhand recently. Access is limited at best, and now you are clearly making bad excuses for Apple making an inexcusable design decision that will cause the laptop to be less useful and to become obsolete even sooner than it otherwise would.
And I don't know about you, but I go to meetings constantly where the closest adapter is on the other side of the room. Ever have to travel to a client? Or take a meeting in a restaurant, or go to a conference where you want to take notes (let alone a courtroom)? I do, as do many other "pro" users, and I sure as heck can't assume they always have power conveniently situated - you are choosing to simply assume away a need in order to justify eliminating a useful feature. A need that every other laptop manufacturer acknowledges in its product, and that EVEN THE GREAT APPLE ITSELF acknowledges in most of its other laptops.
And are you seriously arguing that the addition to the cost of having the battery use the same shell design as the notebook is as much as the cost of an additional power supply and the extra weight of a whole secondary shell for an external battery?
Come on, get serious - I really WANT a new 17" MBP, but this is being an over the top apologist for Apple. I shouldn't HAVE to rely on third party solutions which are utterly lame compared to being able to simply swap batteries as almost every laptop on the market allows.
I guess this goes to show what lengths the Apple true believers will go to though, maybe Apple would be right to do it - if the fans will make any excuse and willingly be locked in and buy products with designed in early obsolescence and reduced functionality, then Apple should keep removing useful features and locking people in and the Mac faithful will keep buying no matter what. It's interesting to see people get so wrapped up in a consumer product, makes you realize that what Jim Jones did is hardly a stretch.