The 1.5 hour battery laptop serves (for me) an important niche. You see, I don't actually need a laptop. I need a portable desktop with built in battery backup, which is what the 1.5 hour battery laptop is.
Of course, it's entirely within Apple's prerogative to ignore that very niche market (I would if I were them) and it seems to be working well for them, but every odd ball computer configuration you see was created to meet the needs of at least one market. You are not the target market for the desktop replacement laptop. I am.
In college I loved my desktop replacement. This was before wifi was campus-wide, so bringing my laptop to class didn't give me much more benefit than bringing a pad of paper, so the laptop stayed firmly put on my desk all semester. What was really important to me was being able to haul my computer out of the dorm in one trip. A desktop would require multiple trips and would need to be shut down to move (the laptop lasted and hour on battery and 5 hours in sleep mode). A desktop replacement offers almost all the benefits of a desktop, but with a built-in UPS and a one-piece form factor.
Of course, it's entirely within Apple's prerogative to ignore that very niche market (I would if I were them) and it seems to be working well for them, but every odd ball computer configuration you see was created to meet the needs of at least one market. You are not the target market for the desktop replacement laptop. I am.