Are you willing to pay 23%[1] more for the convenience of not having to open a window? Because Apple's 30% cut introduces a new cost into the system. Dunno about you, but I'll almost always take the 23% discount and click a few extra buttons.

[1] 1 - (1/1.3) is the additional percentage that must be added to a price maintain constant revenue.[2]

[2] To be pedantic, Apple also handles payment card processing, which is ~3%. So the difference is really 1-(1.03/1.30) = 20.8%