Until the 4E PHB and with the only exception being the OD&D material the week it was originally released, I have not seen any Wizards product in the top 15 products at DTRPG. All their 3.X PDFs are generally available at full MSRP of the physical product.
White Wolf generally has 5-10 products in the top 15 and usually hold the #1 slot.
Right now, the top seller list at DTRPG stands as:
01. 4th Edition Players Handbook
02. Scion Companion Part Two: Manifestations of Ichor (Scion)
03. 4th Edition Monster Manual
04. 4th Edition Dungeon Master's Guide
05. Agent X: One-Man Army
06. Daughter of Nexus (Exalted)
07. Book of Experimental Might
08. H1 Keep on the Shadowfell (4th Edition Adventure)
09. Ruins of Ur (World of Darkness)
10. H2 Thunderspire Labyrinth
11. Book of Experimental Might II: Bloody, Bold, and Resolute
12. Scion Companion Part One: Tuatha (Scion)
13. Scion Companion Subscription
14. The Compass of Celestial Directions, Vol. IV—The Underworld
15. Traveller Main Rulebook
Emphasis mine. Presently WotC have 5 out of the top 10 slots.
Here's RPGNow...
01. 4th Edition Players Handbook
02. 4th Edition Monster Manual
03. 4th Edition Dungeon Master's Guide
04. Video Game Magic Items
05. Starmada: Dreadnoughts
06. Castles & Crusades Players Handbook 3rd Printing
07. H1 Keep on the Shadowfell (4th Edition Adventure)
08. E-Z DUNGEONS: Borderland Keep
09. Book of Experimental Might
10. H2 Thunderspire Labyrinth
11. Legacy of Maela: Campaign Setting
12. Book of Experimental Might II: Bloody, Bold, and Resolute
13. DRAGON TILES: Dungeons of the Dwarf Lords
14. Legacy of Maela: Remote Regions
15. Warcosm PDF
Again emphasis mine. And again, 5 out of the top ten (including the top 3).