I think the author who has a stockpile ready once the first is accepted - is pretty much par for the course. Another CC member - who writes MM BDSM has had that happen to her. One novella accepted and they leapt on the others she'd already written.
I think for epublishers - there is less pressure on authors. I had a few chatty emails from one editor asking when she could expect my next but there was no pressure. Its different for the print guys who have to work to tight schedules and plan things years in advance. The epublishers don't have to do much more than space out their author's releases.
The fact that I had several in my pocket has taken off the pressure - in that even if I had a book accepted today - it wouldn't be put out for several months. So technically, I need to keep writing to keep up a reasonable publishing schedule - and that is more to keep in the reader's mind than anything else. I have heard of writers pushed by readers to write faster, write more of the same, etc. - not happened to me yet!
The other interesting thing is with more than one publisher to write for (the case for ebooks and not print) - how do you decide who to write for next?? You're usually tied in to one publisher for certain types of book. The contracts mean you have to submit each subsequent work to them. I feel now it would be tricky for me to write paranormal for EC - even in a different series.
But I think all this is easily handled by writers without agents. It's in the print world that you need their help. But with that help comes pressure.