It absolutely is up to Sony.
They could simply issue a mandate that states any updates need to be free.
The fact that one of their representatives stated they may charge for some of their first party games shows what mentality they're adopting though.
Time will tell, but should Sony try and ask for money for a performance update I'll be done with them for good. I'm only one of millions granted, but I won't bend over for them.
Either way, you won't get the upgrades on those games then.
Any developer who wants to monetize this patch, isn't going to bother if they can't.
If they try, don't buy. The game you bought still runs at the framerate and resolution it always did. You didn't buy it with an expectation of getting a boost to either down the line, I hope.
This is only for legacy content. Dusting off that code base, and in some cases brining in a new programmer to try and figure this out, is going to cost the developer money. Then they have to go through all the usual q and a and certification etc, and that also costs money.
Most will recognize that this is going to boost sales of their game, and bring with it consumer goodwill if they don't charge for it.
Maybe some won't.
I don't see the logic in blaming Sony. Again, all you will achieve is how ever many games were going to offer this upgrade for free, will be the only games that get the upgrade.