Agreed, and it also doesn't really make sense in this context. In other words, even for those people who do know what "blockchain" means, that doesn't mean they will understand what "Welcome to the Blockchain" means. I think what they were trying to do was advertise Steemit's ability to enable people to get involved with the Blockchain with a very limited investment, but that's not at all clear, which means it's not a very good tagline. I think that promoting this aspect of Steemit (as an easy way to get involved in Blockchain technology) is a good idea, but doing it there in that way is not.