HIBs are a success because of many factors, and DRM-free is one of them.
Other bundles (like Indie Gala, and even Indie Royal) sell only up to 30k of games, while HIBs up to over 400k, no less than 130k.
And if you think DRM-free factor is not important, then you are clearly wrong. I'd not even look at those if they were Steam-only games. And I'm not the only one.
Heck, I don't even have time to play HIB games, I buy them just to give some money to the developers who went with DRM-free.
While concrete figures are not available for Indie Royale, the Valentine's bundle has only sold around 24,000 bundles à $4-5, so a generous estimate would be $120,000 there as well.
Well, this IndieRoyal is also the first one which has two Steam only games (not counting Serious Sam Bundle, because it was something extra).
And as it's less than hout to the end, this is the worst selling (again, except Serious Sam Bundle) Indie Royale Bundle. It won't cross 24k, while with onlt one Steam-only game they always crossed over 27k, and with better bundles they crossed 30k (twice).
(I think this one would count as 'better' too).
Maybe it's not that big difference, but it's still 5k less bundles sold.
I've bought every Indie Royale till now, but I decided not to buy this one.