I've heard that Phillip Quast doesn't want to do Broadway for some reason. Not sure about Denis Lawson. (Incidentally, I loved Quast's performance when I saw the production.)
I think those complaining about Lawson or Quast not being in the Broadway production have to remember that this Broadway revival has a different set of challenges than the current London production. Broadway's 2010 La Cage has to overcome memories of the indifferently received, soft-selling 2004 revival.
If Kelsey Grammer brings media attention and advance sales to the Broadway production (not to mention that he should fare well with the role), then it's some insurance that people will come in the door for Grammer and then discover and fall in love with Hodge.
Begin at the beginning and go on till you come to the end: then stop.