Yep, that's a huge problem with "sustainable" OSS: it's wonderful to get a one-time $50k grant but if you expect to spend the next 10 years maintaining a reasonably complex/sized project, that $5k/yr is still minimum wage.
It is a grant, not a salary. Generally grants are expected to be used for a year or two and you then look for another grant. At least, that's how it works in academia. Not many grants yet in open source so this is harder to make work :/
I don't think there's any expectation that $50k will fund 10 years of development.
No, but "I donated $10 3 years ago and you guys are SLOW at responding to my queries!" is an incredibly common attitude. Open Source has shown that it's a far superior development methodology, but there is definitely some negativity associated with "expect stuff for free"
For a lot of OSS projects users who have donated feeling entitled would be a good problem to have. There are plenty of users who feel entitled and they don't donate time or money!
At present most of necessary software (OS, browser, office suites, social apps etc.) are free in one form or another, so users get in the habit not to pay for it and expecting additional features they want for free.