Incorrect assumption on your part that England are a good ODI team because they are a good test team and that West Indies are a bad ODI team because they are a bad test team, in my opinion. Apart from the fact that the selected bowling line-ups for England were quite different from the tests and ODI's, there's just the fact that England have not exhibited the ability to play ODI's convincingly for a long time. Minus Flintoff and Pietersen and Collingwood, it seems most of their batsmen gift their wicket away when the pressure of 50 overs is on them. The same batsmen (Cook and Bell, for example) thrive when the unlimited overs of test cricket is around them.The West Indies can't be that good a ODI team as their actual side hasen't changed much, since the test series. England should be able to beat the West Indies as easily as in the test series, because we made their bowling and batting look very ordinary during the tests, so why can't we be just as convincing as the tests.
West Indies also have bowlers who have got the variations to cause batsmen trouble (like Bravo and Smith), as well as the part-timers (Gayle and Samuels) that can cause trouble over their 10 over spells. My final verdict is even if the teams are the same, every player has a different rating between tests and ODI's.