No-xp games don't have to be episodic. I'll grant you that I'm running my first no-xp game right now, so I can't speak from experience, but even if you want to run a free-form type game, you can run an xp-less game by just deciding amongst yourselves when it's time to level up. So maybe your players decide to divert to Emmerson lake, they do some exploring and some good deeds and maybe clean out an evil cultist temple or two, and then ding, time to level.
Oh, I agree completely, the DM doesn't have to choose episode conclusions for levelling up. My point was though that players who want to metagame will find a way to metagame, and if the "level ups" seem to occur at the conclusion of episode arcs, then the metagamers are likely to act accordingly.
Just as DM's who use no XP systems do not have to make the levelling mechanic episodic, DM's who do use XP need not award XP for every fight, social interaction, etc. In the latter case, when the party says "Hey, we only need like 300 XP to level, lets go look for stuff to kill in the forest before we enter that dungeon" the DM doesn't have to award XP if he feels that the players are just metagaming in order to gain their new abilities before entering into the the Dungeon of Ultimate Dread.
In other words, metagaming sucks from the DM perspective, but its pretty difficult to completely prevent it. Heck, just tell the players that one of the monsters is casting a spell and odds are that even those groups who don't metagame much are likely to jump all over the caster (at least in my experience) who cares if said caster actually has anything useful to offer to the fight.