You can look at it two ways.
1. LEGO is removing characters from the potential lineup and making them exclusives for the sake of having exclusives.
2. LEGO is taking characters that will never fit into the lineup anyway and making them a limited available item where they otherwise wouldn't exist at all.
Either way, it looks darn-near impossible to get a full set of these even if you attend the whole weekend, and that's frustrating. 1000 of each at SDCC, where capacity is around 125,000 people, is super-limited. The way they're doing it is fair in the sense that scalpers won't walk away with all of them, but at the same time it'll be hard to get even one of each.
At NYCC last year, they had a small line of about 40 people at the booth, as the giveaway was not really public knowledge. These people (myself and friends included) circled through the line repeatedly, several times over the weekend to get a full set. I ended up with four pairs of Batman and Green Lantern (one for me, rest for friends). Even then, only one of my friends got a Superman (and she didn't let me have it :C). All that said, I can't imagine how hard it'll be to get these if it's a one-entry-per-person raffle. Best of luck to anyone trying.
Exclusives are fun to have, but frustrating to get if you're a completist. They say these minifigs will never be in sets, but that doesn't mean the characters won't. I can't imagine they'll never do another Venom, Spider-Man's most popular villain.