Numbers don't tell the whole story. For one, you can probably assume that those 30 million Next gen's also had last gen machines. That leaves you with 90m wide market for last gen. But how many of those 90 million have both 360 and PS3? How many don't care about gaming anymore? How many are double purchases or triple purchases? What is the attitude of the 30 million PS4/XO vs the demographics that still have not bought a next machine?
I'll wait for the sales to come in to conclude what I speculate. But consider it improbable that PS3 copies would even hit half the sales of the PS4 copies. The decision to have it on 360/PS3 probably came a really long time ago early in development. When the forecast was a bit cloudy on market adoption for the PS4/XO.
x360/PS3 games hardly make the charts anymore and are dwarfed by the PS4/XO counterparts.
Go check the financial reports for some publishers. Last financial quarter (3 months ending 6/30/14), X360/PS3 still brought in far more revenue for EA than PS4/XBO.
XBO/PS4 - 293 million USD.
X360/PS3 - 543 million USD.
For the financial quarter before that (Jan. - Mar. 2014).
XBO/PS4 - 172 million USD
X360/PS3 - 562 million USD
Over 1 billion USD in revenue for the old consoles so far this year compared to less than half a billion USD for the new consoles.
And that is why. Next gen consoles software sales are catching up, but for most publishers X360/PS3 still dominate.
[EDIT]
Oh and if you were wondering about Activision who publishes Destiny.
Last quarter (3 months ending 6/30/2014)
PS4/XBO/WiiU - 137 million USD
PS3/X360/Wii - 342 million USD
PC - 182 million USD
Online (WoW basically, so PC as well) - 195 million USD
For the 6 months ending 6/30/2014
PS4/XBO/WiiU - 245 million USD
PS3/X360/Wii - 889 million USD
PC - 281 million USD
Online (WoW) - 395 million USD
There's no way they are going to throw away console sales on X360/PS3 yet. Not when 2014, PS3/X360/Wii is likely to bring in 1.5 - 2.0 billion USD in revenue for Activision-Blizzard.
Regards,
SB