There is an inherent difference between Gen-X and "Baby Boomers".  The term Baby Boomer simply implies a certain generation,  while "Gen-X" implies not only a generation or age, but an attitude or lifestyle, as well.  Most people I know who belong to the generation/age group don't buy into the gen-x attitude (the whole "Slacker" thing...) which  is why they prefer not to be labeled as such.