I guess maybe people who are not using dashboard are also not using notifications centre either!
So Apple is forcing the choice. I'd swear this is to force people to use it right!
For fun. I went and set "Dashboard as an Overlay" in preference (I never liked when it became a space but it's nice to have it as a option, it was set as default I think in Mavericks and I ranked until I found it the fix in preferences), ah the focus, the drop in and fade transition. FOCUS. That's pretty ZEN if you ask me, minimal UI, is NOT Zen.
Minimal in UI does not automatically install calm and efficiency. It's the fashion these days (Google are not winning it either, worse if you ask me) but a lot of people are finding it awful - our minds and visual perception is far more capable of processing more, more subtle more please, more detailed more please, no one wants to stare at a white wall except for the expectational crazy or brilliant who like to imagine.
So much potential. We are better at manage the abstract layers in our minds than visually picking out details on barren flat all UI, complexity is ok if it's done right. I wrote before and I'll write again, never have so many pixels done so little work (Retina) in a UI.
More is doing Less.
Removing utility is not improving things, it's like going beyond the fretless neck on a instrument, removing the frets is to far for many, removing the
strings! - think: laser stringless type guitars, did they catch on? No.
I rest my case.