Exactly. Simply put - we can only guess on why apple chooses not to have user-replaceable batteries...but in the end it is purely guessing and nothing more.
Not true at all.Check out the unibody macbook keynote,and probably ad copy on their site.
As others have correctly stated,
1 Larger batteries are possible by eliminating the case parts associated with removable batteries(springs,doors,etc.).
2 Odd shaped batteries can be molded to to fill available space.
3 Removable batteries must have their own case/packaging,further wasting space and capacity.
4 Battery technology has progressed to the point that the majority of the time,it lasts the life of the device.If replacement is needed,Apple feels the (IMO)reasonable cost of replacement is worth the other advantages.
5 Because of the above,the device can be thinner,lighter sleeker(This
IS Apple ,after all!),and have a superior battery life.
So to sum up,Thinner,lighter,sleeker,longer battery life.
No guessing there,just info straight from Apple.