Many people say: "No problem, it is anyhow a decision by the server and this side will choose a strong encryption." But the weakness here is the problem you described.
You absolutely should configure all endpoints only to use adequate cipher suites, but that's simply because the bad ones shouldn't be used and as a client you don't want to rely on the server being well configured (and vice-versa).
HOWEVER - that does not mean a handshake MITM is possible, the protocol accounts for this, please see my parallel reply to yours.
There is no additional hashing involved.
Some of these issues are addressed in later versions. But. And there is always a big BUT: http://f0rki.at/static/slides/f0rki-downgrade-attacks-by-exa... I will now not got through all the published informations or talks from BlackHat, CCC, and so on. ;o)