Okay, so the only authority you are citing is the one in your own world. I'm glad I'm not violating any authority recognized beyond that world.
Writing/typing/chiselling in stone a note is what matters, not the medium with which it is delivered. If someone doesn't have email, then a handwritten note is sent. I would agree that a text w/all it's b*****dized English is not acceptable.
The issue at the heart of the matter is the showing of appreciation for the gift, and yes, that is becoming threatened. However, you can continue to think sending a handwritten thank you note makes you better than everyone else; the rest of us in the real world know the opposite is true.