Not sure if you've had a look at Vgchartz numbers for the DMC series.
http://www.vgchartz.com/gamedb/?name=devil may cry
DMC1 is at 2.99 mil, yet Capcom have reported 2.16 mil.
DMC2 is at 1.97 mil, yet Capcom have reported 1.8 mil. Which is okay I suppose.
DMC3 and DMC3 SE is at 4.06 mil, despite selling only 2.3 mil.
DMC HD Collection is at 1.17 mil, despite selling less than 1 mil.
So while DMC2 and DMC4 are close, Vgchartz numbers for the DMC series are very inaccurate. There is no excuse for this either, Capcom release their sales data publically every year, other publishers don't do that. Vgchartz have no excuse if I can find the right numbers from Capcom website by just typing stuff into Google.
So I disagree, Vgchartz sales numbers can't be trusted in this instance.