but I'm fairly certain Mario doesn't
Sales-wise, it does easily.
Bzzt! Not even close. This is data from VGchartz.com for the first 10 weeks of sales in Japan for each of the following games:
843,123 Super Mario Galaxy
721,828 Super Mario Galaxy 2
3,474,680 Dragon Quest VIII
3,887,903 Dragon Quest IX
3,546,530 Pokemon Diamond and Pearl (combined)
3,003,570 Pokemon Heart Gold/Soul Silver (combined)
4,507,127 Pokemon Black/White (combined)
Dragon Quest and Pokemon are very comparable in terms of popularity, and Mario isn't even remotely competitive.
I see your "bzzt" and raise you one in return. 3D Marios fail at sales in Japan pretty hard (and even in North America lose pretty decisively to 2D Mario). So, we stroll over to 2D Mario and we see...
DS New Super Mario Bros. 5,187,000
Wii New Super Mario Bros. Wii 4,281,869
While we're here, it's worth noting that a couple other DS games sold comfortably more than any DQ:
DS Brain Age 2 4,865,000
DS Animal Crossing: Wild World 4,654,000
And this is just sticking to games released in the past decade. The best-selling DQ game ever is pretty much a tie between 7 and 9 (aside: oh man, that does not help my respect for people's tastes) but Pokemon and Mario have certainly hit greater heights in the past which DQ doesn't even approach.
GB Pokemon Red/Green/Blue 10,077,000
GB Pokemon Gold/Silver 7,961,000
FC Super Mario Bros. 6,810,000
(Sources: NSMBW is from VGChartz, which I don't like to rely on since they're not known for being trustworthy, but I did find several other sources confirming that Japanese sales of the game topped 4M, so in this case the numbers at least seem plausible. Other figures are from a quote from Famitsu found
here.)