In addition to the principle Karunamon mentioned, made up names have greater protection than words in common usage. Microsoft isn't as exotic as Xerox and Kodak, deliberately completely made up, but it still gets a greater degree of protection than, say, Apple.
In everything I've ever done or been involved with in startups, I'm not sure anything besides people was more complicated than trademark law.
Unfortunately, my Amazon search and Google fu isn't good enough to find the book I learned most of this from, but if you're really interested in this, it requires a book level and length treatment. E.g. did you known Owens Corning has a mark regarding the color pink? (Only, or at least originally in the context of insulation.)
