I think this is one of the best quotes to keep in mind about the Surface Pro and comes straight from MS “If you compare it to say a MacBook Air, you will quickly see that pound for pound in battery size vs. battery life, you will find optimizations that puts Surface best in its class.” You really have to look at it pound for pound and not tablet shape for tablet shape.
The other thing they have done which is so innovative people haven't really picked up on it yet or figured out how to make the best use of it is the quick charge battery. One of the articles I read says that other manufacturers have picked up on the idea though and we can expect to see it in more products going forward. So yes your device "only lasts 5 hours" but you can also get 50% of that back from dead empty in an hour. If you can find one hour a day to plug your device in during your real world use time goes up to more like 6-7 hours plus the one hour plugged in.