Don't hold your breath. You can record whatever an internet browser is playing (or any other application, basically) using third party programs. There isn't a defense against this on Pandora's end.
But when you record an MP3 and then compress it again to MP3 you've then doubly compressed it with a lossy format. Besides, I personally feel like, if someone wants to go to the trouble to record a song streaming from Pandora, who can really feel threatened? If you've experienced buying and shopping for music legally, it's a pretty nice experience. You can browse everything and it's nicely organized. You can get full album art and correct ID3 tags. You can choose the explicit versions of albums. Pirating music really isn't that nice of an experience. And if you really want to support an artist, just buy some merch or go to a show. And for independent bands, the Pandora plays and especially album sales is real money (if you sell an album for $10 online, the band makes something like 50%). It actually feels nice to pay for things especially when it's obvious that as a whole, these talented people make almost no money on average. But more than being altruistic, it's just nice to be a part of modern culture and follow bands, much like people follow sports. Getting some new album and reading reviews and going to their shows is really just a lot of fun.