Your friend was exactly right about the yeast. If you look at the actual recommended numbers from the Mr. Malty calculator, if you have yeast that is 97% viable (basically if it's pitched the same day it leaves the lab, the stuff I get from my LHBS is usually closer to a month old by the time I get it, and more like 75% viable) one vial is an appropriate pitch for 5 gallons of wort only as high as 1.028. In practice, if I have very fresh yeast, I'll go up to 1.040 without a starter, and anything higher than that, or anything with older yeast, gets a starter by default.
Not making a starter shouldn't have too much noticeable impact on your FG unless you're going to an extreme level. Rather, the yeast will have to grow more to reach the right level for fermentation, and in doing so can create a lot of off flavors, the first you'd notice would be additional fruity esters.
I would follow Mr. Malty's calculations to the letter for the time being. The guy literally co-wrote the book on yeast.