Some people are not bothered by short battery life. I think what does matter is that it's a unit they are comfortable with that delivers what they need. Obviously someone who travels a lot or can't charge batteries at their job will need something with long battery life. But not everyone does.
Fact is, a 510 and a PCC will be just fine for someone at work all day. This past Sunday I went to a friends house and was gone from home for 14 hours. All I had with me was my 510, my PCC (with one spare battery in there charging), and my juiice. The PCC case stayed charged ALL day long and every 3-4 hours I'd put the depleted battery in it, take the fresh battery out. And I was puffing away like mad all day. I would think someone at work would be too "busy" to puff as much as I do (4-6 sec drags every 20-40 seconds), so one battery for them would probably last even longer.