I'm sorry Kath, but I have to disagree with you for once.
I mean, I know what you're saying, and you're right, that actually is the actual defintion of "lame", HOWEVER, the term "lame" is one of the MANY words in our vocabulary that has been taken out of context in recent times (like "literally", "epic", "ultimate", even "gay", etc)... the fact of the matter is, people don't even actually use the term "lame" to describe a person with a bad leg anymore, they're usually refered to now as "handicap" or "diabled", wheras "lame" is used to describe something that's pathetic, mediocre, lack-lusting, unimpressive, etc.
Again, it's all a matter of the context the word is used in.