The rejoinder would be that, unlike my bartender, I could conceivably have 100,000 people tip me $0.25 through Gittip. When you compare $0.25 to a Facebook "Like", it's a lot more valuable.
That said, I appreciate people who want to make even more on Gittip than I do. Go for it! :-)
>> unlike my bartender, I could conceivably have 100,000 people tip me $0.25 through Gittip.
And if the minimum were $1 or $5, I don't see how that's a problem. Your bartender doesn't have global reach and his/her services don't have infinite scalability. The bartender/dry cleaner/barista examples were to illustrate lower bounds and not the maximum.
There's no reason to place artificial ceilings on how much developers can make with something like Gittip.
That said, I appreciate people who want to make even more on Gittip than I do. Go for it! :-)