Compared to Apple’s outrageous 30% from the same service, Google approaches the issue in a much more humane and thoughtful way.
You should also remember it’s only around 50k of the total apps in Market that are paid apps (compared to AppStore’s 200k!), therefore Google puts a lot less pressure on the devs and service providers…
Amazon, Netflix (if it actually starts working on Android), all the online news services, like NYT, BBC, The Daily and everybody else providing in-app purchase for Android will find this small fee benign and suited for their common objectives.
I’m also confident this is the correct approach Apple should have taken some months ago when they decided to cut the wings of all the publishers, editors and developers that were misleadingly attracted by Apple’s initial proposition of free in-app purchase; instead, Apple went for the unattractive, show-stopping, devs-ruining 30%.