Well, Safari5 Reader's approach may make that feel less necessary - since one can easily click in and out of Reader-view.
And an advantage (as I test-drive it) is that turning the Reader-view on/off for a given article is almost instantaneous: whereas with Readability to move _out_ of Readability-View involves _reloading_ the entire page (which I find annoyingly slow on pages like TechCrunch, RWW, etc where there are tons of ads to be (re)loaded.
I think the Safari-Reader approach may increase time I spend with a full, ad-laden page open.
Because non-print versions kinda blow. Spanning a single article over 10 pages with a few dozen words per page just so you can get 10 times the ad impression is not acceptable.