I think you mean the only way you can get Netflix is if you 'upgrade' your firmware. If so, then you are correct as far as I know. I know a while back Netflix was sending out free PS3 Netflix discs, which is where I got mine. The only thing is, you have to pop the disc in every time you want to use Netflix. Kinda gets to be a pain in the ass. But yea, I'm not sure if they're still handing these out or not. You might want to look into that.
But other than that, yes, you'd have to upgrade to get the 'discless' version of it. It IS very handy but... Once you upgrade, there's no going back. From that point on, your ps3 is in Sony's hands and your system will get further raped of it's features. I wouldn't reccomend updating but if you feel you desire discless Netflix that bad, then by all means go for it.
As far as getting rid of the jailbreak, all you'd really have to do is delete all the homebrew you've got, games, etc... Then just never jailbreak it again, it's that simple.