I have 3 non-Rendo email addresses, that are used only for specific clients, that got that spam
message.

Email adresses from private servers you manage yourself, or ISP addresses? Many ISPs (may their souls burn in hell) resell their client's adresses...

I've got the feeling that the only answer which will satisfy here is:  "Yes!  Renderosity got hacked!
  Let's all panic together now!"

No, the only answer which will satisfy here is one explaining that coincidence. The "hacking" headline was just to attract attention, as I said; I don't believe it.  It's more likely a case of an intern misusing the client e-mail database or somesuch; I've already seen this.
I don't believe Rosity might have the stupid idea selling it's client's database, as that would be shooting their own leg - with an RPG (that's a Rocket Propelled Grenade, not a Role Playing Game...).

As about you people not minding spammers - You are apparently quite new to internet. We'll talk again when you reach the point of recieving several hundred spams/day, and you have to invest thousands of dollars in hard & software to keep your company's e-mails halfway useable... Spam severity always increases, as spammers exchange their victim's adresses (which makes that you might recieve the same spam a dozen times in a row, if your address was included in a dozen CDs).  Once an address is compromised, you can only delete it and create another.  :-/