I hope you had fun playing D3 on launch day. Or any other game that required a server connection.
Blizzard's SC2 HOTS just came out, I was at the launch party and then got home before midnight for the servers to come online. There was a friendly warning on the login screen saying that there was scheduled mainenance from 11pm to 1am, to cover their ass in case of outages, but the maintenance only went from 11:30pm to 12am, and I was able to play without issues immediately.
The original SC2 WOL's launch was just as uneventful.
The only issue that I've seen with HOTS is that they decided not to put the files on the physical disk, so people who didn't want to buy the digital edition basically have been tricked into buying it anyway.
In the MMO realm, I played Guild Wars 2 on release not too long ago, and while it was completely packed and overloaded, they had mitigation strategies in place. When a server was full, new players were simply put into another shard of that server, and then queued to connect to the 'real' one. You could still play the game fine, you just had to wait half an hour after connecting to be put in the 'real' server if you wanted to play with your friends. Alternatively, you and your friends could look through the server list for one that wasn't at capacity. Personally, I didn't have any issues at all -- not like D3
Disclaimer: I work for EA also, but also unrelated to this project.
Server problems are to be expected on launch day. It happened with Diablo 3. It happened with GW2. It happened with Castle Story. I can't (off the top of my head) think of a game that had zero server problems on launch day (although I'm sure they're out there). If you buy a game, developed by any studio, that you know needs to connect to a server expecting not to see any problems on launch day you're living in a fantasy world.
EA's own Battlefield 3 (PC version) had minimal issues on launch day, because they actually tested it properly. I mentioned this earlier -- they actually stress tested how their infrastructure held up against X-million users before launch (using 'the cloud' to simulate their horde of users), and kept fixing all the load issues before release. On launch day, they simply knew it would work, having already seen it been hammered by X-million concurrent users, and had methods to increase/decrease capacity at short notice, if needed.
That said, there were excess-load issues with the 360/PS3 version on launch day, but it's a bit harder to rent a million Xboxes for pre-release testing, and they're on a restricted internet channel, so it's a bit more forgivable for them to screw up in that arena.
It's not at all a fantasy to expect that things work. You're selling a product, which makes promises on the box. If a consumer takes that box home and the product doesn't deliver, then you're at fault.
If you expect that the first batch of your product may be faulty, you need to write that on the tin.
The number of concurrent users in a game is likely higher on launch day than it will be from then on as people who have pre-ordered etc try to get in to play for the first time. Therefore paying to set up infrastructure that you won't need x days down the line seems extremely inefficient.
Assuming you're using commercial data-centres, then it's not like you have to go out and buy a whole bunch of extra equipment for that day and then decommission it later. Most data-centre resellers can spin-up or decommission any number of servers within 15 minutes to 1 hour. If you're tracking pre-order and real-time sales data, then you can figure out an ideal upper bound on the amount of server hardware you'll need on launch day.
Two days later you can shut most of it down if your active users has dropped.