I don't want to be rude but...
If the guys at Steam are so cooperative, can't you make some sort of steam key for the people who have Season 1. I don't want to be disrespectful, but what if telltale vanishes in say 3-5 years, or in one year I totally forget about the company and just have the pleasure to remember the game? Or I lose my mailbox... It's not like I have a hard copy of it, put the CD, read the cd-key on the box (no internet activation) and play the game in 5 years from now. Steam is much more solid in terms of long-lasting, than telltale.
And for what is worth... I want all my games under one account
Sorry for my bad English.