I think it's a stupid move too, why do a straight adaptation of the book? Hell, if they want to wring the Harry Potter cash cow, why not just remake it ALL over again in Miniseries form on HBO? That way nothing will be left out.
What works on the page usually does not work in film format. Not sure why people don't understand this simple concept.
I don't think we'll have to worry about the "they're too old" thing, as long as they film both parts of book 7 back to back (a la Back to the Future 2&3, or Pirates of the Caribbean 2&3), which they will given its release schedule of 6 months apart.
In any case, this is a wise move to please only the more slavish fans of the novels and to put more money into Warner Bros.' coffers. After the crapfest which was Order of the Phoenix, both parts should be coming Blu-ray direct to my mailbox via Netflix (or on demand to my Ps3-TV) in late 2011, after I head home from a fun day visiting Cars Land at DCA