Hypothesis: The PT came first, thus being known as the OT. The Sequel Trilogy was made later.
Outcome:
Lucas really lost the plot with the ST. After all, the sequel trilogy spends almost four hours beating around the bush about Vader's identity. I mean, c'mon, we know he's the father of these two twenty-something "heroes," why doesn't Lucas just come out and say it at the beginning? Why do a "big reveal" to reveal something we already know? Vader's revelation in ESB clearly shocks the Luke character, but the audience feels nothing--except perhaps a little mocking derision towards Luke--because we've known this for years. Yawn.
The sequel trilogy's lame attempts at pacing also touch Yoda. Yoda is introduced as a mysterious figure in Empire, and successfully tricks Luke into believing he's a crazy old hermit. (Aside: What an idiot this Luke kid is! Nothing at all like Anakin.) And then there's a "big reveal" when we discover that Yoda is Yoda. Big deal! We in the audience have known who Yoda is for decades, Luke just looks stupid for not knowing that. How much ground from the OT do we have to cover before these new characters are up to speed?
Lucas tries the same boring "slow reveal" thing with Jabba and Palpatine. They get talked about in the first movie, then you briefly see Palpatine (or what is supposed to be Palpatine) in the second, and finally they are revealed in the third ... but why? We all saw Jabba in Episode 1, and we saw Palpatine in all three of the original movies. Treating the ultimate villain as something to be slowly revealed is just melodramatic and lacks the cinema verite quality that made the original Star Wars trilogy so great, doing away with all those pretentions of dramatic structure.
Finally, the last scene in Return of the Jedi was just insulting. After two GREAT performances by Hayden Christiansen, he's replaced by a geriatric no-name with a dopey grin.
So, yeah, the ST sucks. But what really sucks is that Lucas refuses to release the OT in it's original, unaltered format. If he puts Sebastian Shaw in Attack of the Clones, I may scream.