There is no reason they could not make a removable batteries with the same performance characteristics.
Also, that 7 hours can only be achieved when the battery (not the computer) is brand new. As the batteries age their ability to hold charge diminished. The other downside is you cannot carry a spare battery for your laptop.
The upside for Apple is that in a year or two when battery life starts to get shorter you might consider just upgrading to the next model versus sending your old model in for a battery swap.
I don't think anyone offers a real notebook with the form factor of the MBP, with 7 hours of battery life.
The battery life will decline over time, but that is the same for all batteries. The rated lifetime of Apple's batteries is 1000 charges, 2x of regular (of course we will see how well they really hold up.) I understand that there are only minor form factor improvements by making the battery internal, but whatever the difference the battery life of my MBP is really, really good.
The battery is actually easy to access, and it's only a matter of time before 3rd party batteries are available. The main inconvenience is not being able to easily swap in a fresh battery when no power plug is available. But I've never even owned a backup battery for my notebooks, so given the existing choices out there, the new MBP is my personal preference (given that I will be able to replace the battery myself when the time comes.)
If you don't want to swap it yourself, Apple charges $129 for the service. Definitely a bit steep, but I think the regular removable batteries for older batteries were not much cheaper (I never bought retail so don't remember exactly.) Apple's and Panasonic's margins on batteries is probably similar.