By forming two different PvP game types you segregate the community.
"What rank are you in PvP right now?"
"I only play non-ranked."
That's how it'll happen.. This is a reason they don't want an E-sport. Not to mentioned the need for the separation of auction house gear for each PvP type.. Just between those two changes you'd split the game another four ways, farther separating parts of the fanbase.. Hardcore mode is understandable since it's a whole different style of playing the game. A ranked PvP will be no different from regular PvP in play style.
Also the reason PvP is so prevalent in D2 I find to be painfully obvious.. The game is very old, all the the content has been played out, played again, beaten dead with a paddle, resurrected, then shackled to a rock and left for the birds; the only thing left is PvP.. Blizzard North was very slow, and under-par with their expansions, and content additions. Blizzard is known for having full and challenging expansions, not to mention occasional content additions on the fly to keep things fresh. Diablo 3 won't be left to slowly wither away was Diablo 2 was.
I feel Blizzard's choice so far to avoid hyper a competitive PvP environment is for the best of the fanbase as a whole. Being as non-bias as possible, seeing as I support the choice, I feel in order to be competitive, you have to save stats. Be it win/loss ratios, K/D ratios, fastest kill time, or any other in game happenings, the fact is that no one wants flaws saved on their account for anyone and everyone to see. People obsess over these smudges on their record so much, they'll buy whole accounts for loads of money with better records just so that number 75% turns into a 87%. Frankly, I feel there are enough E-sport games out there right now between console and PC.
On the second tier of reasoning, one could mention that with the real money auction house in place having a competitive atmosphere would lead to people buying more ( <- key word here) items from the auction house, or third party sites. Yes, people will be buying items to win PvP matches, but if you increase the competitiveness that number of people buying items will sore. Is this necessarily a bad thing? It could be, but that's not really the point. The point is it would be fueling a concept that Diablo itself doesn't stand for, and the development team doesn't see fit for the game as a whole.
All and all I will enjoy PvP as just another way to play my character, not to keep a tight win/loss record. All the more reason I support a noncompetitive PvP system.