I'm not really sure what to say about this. Obviously this is part of the emotional fallout from the Rasmussen saga; whether it speaks subtly to some aspect of that (e.g., De Rooij upset b/c Ras wasn't guilty??) is not immediately apparent. On its face, De Rooij just sounds tired.
I guess this is significant though. Among the Pro Tour teams, Rabobank is a model of stability, and De Rooij has been its anchor (along with obviously the sponsor) since 1995. It hasn't always been clear what Rabobank were up to under his leadership, besides working for Boogerd at Amstel Gold, but they've won plenty of races, put together some really great rosters, and managed to do so with comparatively little scandal. Hopefully Rabo and Dutch Cycling will not suffer from his departure.