Too early for 3 crewmembers ?

Of of Jacques van Oane's message indicated that ESA will be sending a
3rd permanent crewmember to the station on the next Soyuz.

Considering that we current have no idea if the shuttle will be able to
fly regularly, is it wise to begin full crewing so soon, before the next
shuttle ?

Or has NASA indicated to the ISS members that it has very high
confidence that the Shuttle will be in reliable regular service by the
middle of this year and that 3 member crews are sustainable right away ?

Or is it just a question of the tons of supplies left on the station by
discovery's last flight (safe haven stuff) are somewhat perisheable and
sending a 3rd crewmmeber will just help consume those supplies that
would otherwise have to be tossed out eventually ?