I think the whole big studio movie thing is a complete lie. Just look at Brandon Routh who had to step into the red boots of arguably the most popular comic book character of all time; Routh didn't even have one big movie before he played Superman. Also, Bale, Murphy, Ledger, etc. were hand picked by Mr. Nolan. The director chooses. I don't think Glover was considered, because, honestly, I don't think he would have been that good. Nolan picked Ledger because the guy has serious range; watch Brokeback Mountain. Ledger is smart; the voice, the mannerisms of the joker all come straight from Ledger's formulations. I don't think Glover is any where near as smart as Ledger. Glover plays the same character in every role: A nervous, nerdy, silly, zaney guy. That's all he can do. He's not on the same level as Ledger.