As always, I disagree with Microguy. There are all sorts of domaining strategies. Only some will work but buying .coms is no more likely to work than any other. The fact that businesses prefer .coms and consumers are more familiar with them is in the price.
The question is what will happen next. If consumers become more familiar with certain alternative extensions, prices may go up. If fewer people use direct type in as a form of navigation or if search engines scale back the value of domain keywords in site ranking, there will be downward pressure on some .com valuations.
My belief is over time people will become more accepting of alternative extensions, fewer people will use direct type in as a form of navigation, and domains will become virtually useless for SEO. Increasing alternative extension acceptance will happen because young people with development skills won't have the cash to pay .com hoarders, better search engines and internet information searching skills will reduce direct type in, and search engines are already giving little SEO benefit for domain names and that will continue as algorithms get better at assessing content and backlink quality.
I have tried alot of different buying stategies, including .com, and to date .pro is one of the best. I have recouped 1/3 of my outlay on .pro selling 9 domains and still hold 250. The underlying reason for this is .pros registered have risen from 6,500 to 46,000 in the last 3 years, renewal fees have fallen from $99 to $20 and all professionals in all countries can now register them. This creates more demand for premium .pros on the secondary market and but less supply.