If the test for "top tier" is licensed setting of any consequence, is anybody in the biz aggressively licensing other than Green Ronin? Probably not.
Margaret Weis Productions puts out licensed RPGs for Serenity, Supernatural and Smallville, just off the top o' me head.
Below that, in Tier 2 as far as market presence goes, it would appear that the current best sellers in the market place are Paizo's Pathfinder, Fantasy Flight Games' Warhammer at #3 and then Dark Heresy/Rogue Trader #4 with Green Ronin's Dragon Age RPG in #5 -- in that order -- according to ICV's report on Diamond Comics Distributors sales for the 1st quarter of 2010.
I think you have to be careful thinking about that - you're talking only about a single quarter - Q1 2010 there. That's not a long time.
If I recall correctly, White Wolf was in the same Top 5 for at least Q 2, 3, and 4 of 2009. Are they suddenly not "top tier" because for one quarter they've not been in that list? Even though they've been big in the market in general for many years?
Top tier of what stack?
Top gross sales? Top product quality? Top influence on the rpg market? Top company worth? Top company size?
Are they all top tier? The DC license is particularly promiscuous, having been with three different companies now. She ain't no catch.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.