Interesting point. At present, the reason for
autoconfirmed is
basically to stop certain forms of casual vandalism. You have to do
some preparation if you want to engage in page-move vandalism, which
due to software limitations has historically been more of a pain to
deal with. I would tend to view edit counts as an extension of this:
not only must you sign up and wait, you also have to make some
innocuous edits.
I suspect that if a user is dedicated and sinister enough to plan out
ten edits and four days to get autoconfirmed before going on a
page-move spree, he's probably going to make some whitespace changes
with his ten edits, not vandalism, so I'm not sure this will help at
all.
For page-move vandalism, you're probably right, but autoconfirm also
lets you edit semi-protected pages, and I don't think your point
applies to that form of vandalism.