Generic .com domain names are like diamonds. Sure you can buy a small or low quality diamond and your significant other with still love you, although she will know that you couldn’t afford better. You could also buy a synthetic or manufactured diamond that may pass for the real thing, and maybe she won’t notice (until she gets it appraised of course). However, if you want the most beautiful investment quality diamond, you need to spend the money and buy a beautiful, high-quality, real diamond.
With domain names, sure you can buy a low quality .com domain name with extra numerals, hyphens or other flaw, and people who know about your site will try to remember how to navigate there. You can also buy a non .com domain name such as .net or .info that may look good, but will certainly lose traffic to the better .com name. However, if you want to buy the most valuable, highest investment quality domain name, stick with generic .com names.