Not snipping to get to a point, rather to save space.
Firstly, you are the first person to accurately describe the real issue while raising it to question. D3 is a Multiplayer game with a single player component and has no OFFLINE single player option. This I am personally OK with as I'm only interested in multiplayer and would need internet anyway, although it does suck for those who couldn't care less for the multiplayer aspect.
Most my response comes from a programmer's view of things, and the explanation that best makes sense about the servers as that they set up hardware for the average server load, NOT the first day release. As much as this sucks from a customer perspective, it unfortunately makes complete sense from a business perspective. So, I opted not to play for the first week or 2 myself until the server load gets closer to the average balance that Blizzard (most likely) prepared for.
Even though I haven't experienced anything other than the beta, from what I've read it sounds like they actually did a pretty good job. I expected much worse, even though as a paying customer I shouldn't. The unfortunate truth is this is a company looking for long-term revenue, not to make you personally happy. This is the case with any company.
While I do like Blizzard games, I consider myself more of a realist. So if I defend any company or situation, it is because I truly believe they did well.
As for the gameplay itself, I cannot comment. But boy am I ready to play!