There isn't even an official start date yet, it could be the middle of August for all anyone knows...
On paper it would suggest to be a much better idea to launch in July ready for the Summer holidays, but with so little time to promote already heavily operated routes, where would the sense be in that? Bmibaby will already have thousends of passengers going to those destinations, such passengers won't be cancelling their holidays and changing because bmibabys details have been very clear in that specific dates have been set to their closure.
Monarch have got it absolutely correct, they know Ryanair will find it difficult to put a few extra aircraft at EMA due to little flexibility in their operation this Summer due to limited new aircraft deliveries, Flybe don't have the capacity to offer those routes at the current time on the scale which bmibaby did, and Jet2 are already planning for 2013, so in the near, short term, won't be planning anything different also.