People wouldn't have even been familiar with the concept of Star Wars movies having episode numbers until May of 1980.

As for the title being smaller, that might just be the mystery box at work and them thinking it would be a fun way visually to unveil the title. I'm sure the marketing departments at Lucasfilm and Disney are gonna be busy trying to come up with a catchy-looking logo a la Empire and Jedi. The selling points for all three prequels were the "filling in the blanks" of Episodes I, II and III, hence that was the biggest part of the logos. Episode VII is, arguably, an equally big selling point, but I think they want to avoid anything that will remind people of the prequels in the marketing.

I remain very curious as to how they're going to open the movie without the Fox fanfare. At this point I'm assuming Johnny's just gonna come up with a new piece of music to play over the Disney and Lucasfilm logos and then the rest of the opening will be identical from there.