We (the audience) are linear creatures subject to time, so this is a challenge to explain. Please bear with me. The Storybrooke residents who have been in Storybrooke from the moment Storybrooke was conjured up, have not been in Storybrooke for 28 years. It wasn't just that the clock didn't work in Storybrooke. Until Emma decided to stick around, time itself didn't work there. There were no years. No months. No weeks. No days. No hours. No seconds. There was only illusion. The Enchanted Forestians were magically plucked out of their real world, and plopped into what I like as a mystical holding pattern.
Once Emma decides to stay in Storybrooke, she causes a little crack in the curse. The curse still enchants the Enchanted Forestians, except that now, time passes for them, too. They don't notice this major change though, because before the curse cracked, they were under the illusion that they were subject to time.
The second most important thing to remember is that everything originally in Storybrooke was created as a result of the Dark Curse. The curse affected, and still mostly affects, all the cursed residents of the Enchanted Forest (as far as we know). For example, take the previous episode, "Snow Falls." When Prince James Charming's Storybrooke persona wakes up in the Storybrooke hospital as amnesiac David Nolan, he learns he is married -- not to Snow White's Storybrooke self (whom he doesn't remember) -- but rather to Kathryn. Except? He is not married to Kathryn. Not really.
We don't have to start looking at Kathryn as a liar or Regina's minion. It is most likely that Kathryn thinks she is truly Kathryn, and that she's married to David who she believes is truly David, but it's all a lie created by the spell. This is brilliant, by the way, because it makes her more sympathetic. No, she has no real marriage, but she has been enchanted to believe that she does, so it seems real to her.
We won't have to start looking at Mary Margaret/Snow White as a home-wrecker, or David Nolan/James Charming as a philanderer, once they get involved (that's not a spoiler; c'mon, they're going to get involved). This, too, is brilliant, because who wants the lead fairy tale Princess in this series breaking up a marriage. There is no Nolan marriage, because really, there is no Kathryn and there is no David. Kathryn and David are fake names attached to the Nolan façade magically cast over James Charming and his ex.