I am very puzzled by the designation of David Hyde Pierce and Hank Azaria as leads -- they are on stage a fair amount of the time, but they each play the same character for only about 10 minutes at a time and have just one song. If they weren't "names," no one would consider them to be leads. Christian Borle has more impact and more songs (and possibly more lines) than either of them, but no one thinks he should be in the lead category.
My personal prediction: only one of the two of them will be nominated. Lithgow, Pierce, and Azaria are all extremely good actors, but none of them are strong singers (I don't think Azaria even had an entire song to himself -- I think he only sang about half of the Lancelot song) and none of them can dance AT ALL. I can't see the Tony committee giving 3 of the 5 lead musical actor noms to folks who are neither strong singers nor strong dancers. It would be an interesting comment on what chops you need to get nominated for a Tony for Best Actor in a Musical. That, plus the fact that one would want to spread the wealth, means that I think a DRS/Spamalot strangehold on lead actor is unlikely.
"What was the name of that cheese that I like?"
"you can't run away forever...but there's nothing wrong with getting a good head start"
"well I hope and I pray, that maybe someday, you'll walk in the room with my heart"