It's been shown that BMC folk who are die-hard fans of one brand can't tell the difference between the three in a blind taste-test. Have you actually done this or are you just boasting?A buddy of mines father swore to me that I could not tell which is which in a blind taste test. I could easily taste the difference, it leaves me with a horrible aftertaste everytime.
As flavorless and bland as BMCs are, the "Light American Lager" category is actually one of the most difficult styles to brew. They are so light and low is extreme flavors that off-flavors can show their ugly heads. The styles we brew most likely cover up these BMC off-flavors (what I know exactly of which you speak)I wish I could pin it down enough to know what it is...so I made sure to never accidentally brew it...