2) Regarding "The vast majority of sites don't need to scale beyond a single server," you could make the same point that the vast majority of sites are not profitable either. It's a total non sequitur in either case.
3) Your point that it "costs less" to develop in Ruby which can increase the profitability of your site is an incorrect assertion. It may be true that the time to develop in ruby can decrease your R&D costs, it does not affect your cost of goods sold and has no impact on your margins. If you just say "it costs me $100 less to develop in ruby, thus I've made an extra $100" you need to take an accounting course.
More to the point, if you are building your business with your optimization being focused on decreasing development time, you have already lost sight of the goal.
PHP sucks, but there are a ton of profitable companies that use it because it is wicked wicked fast. In my mind, that makes it suck less. :-)
-David