No surprise they've gone with Cook, it's clear they like the captain to be in charge of Tests and ODI's, and with Cook the very likely successor to Strauss in Test cricket, then having him in charge of the ODI's makes sense in that respect.
My immediate thoughts on this was the same as what people on here have already posted, how can you select a captain that is deemed not good enough to play in the XI ? WI have done the same with Darren Sammy and it becomes a very awkward situation. However, if Strauss is not playing ODI's, then it's conceivable that Cook would be in the strongest XI, if they are going for a similar style of player at the top. There will still be question marks over Cook's ability to succeed in 50-over cricket, but I have always thought there is a place for him in the one-day side on the proviso he scores runs aplenty, firstly with Essex, then when he gets his opportunity for England. Now he simply must succeed at the top of the order for England with the added pressures of captaincy.
It's hard to judge his captaincy in one-day cricket, as he hasn't done a great deal of it. The Test captaincy will seemingly also be his, so this does offer him the opportunity to bed in to the role, throw in a couple of overseas tours where Strauss may be resting, and in theory we will have a well planned, semi-experienced leader ready made to continue the good work of Strauss.