[SPOILERS] DaveV is not clowning around. Well, maybe a little bit...

[Jabah]

you obviously need less fog to decide, but if the sea is blocked by ice, (therefore protected from boating as I understand the potential fear), what is the downside of a city on the coast (plains hill sheep is hardly a food compared to netted crab + lighthouse & commerce options

[DaveV]

A bunch of factors:

1. I usually use ICS spacing in EitB. Cities rarely grow big enough to work lots of tiles and trade route income usually offsets city costs by the mid game. Five tile spacing means I can't squeeze a filler city in between the capital and the new city, also a 1-move unit on a road can't cover both cities. Counterpoint: this game, with nearly 300 tiles per player, is more likely to go to the late game so those arguments are somewhat weaker than usual.
2. Crab is not a particularly strong tile: +1 food, +1 commerce, -2 hammers compared to plains hill sheep. It also requires researching Fishing, investment into a fishing boat when I need ground units, and later investment into a lighthouse to become a 5F tile.
3. Building on the water means vulnerability to Tsunami, ice or no ice.
4. Every move outside my borders increases the chance that a strong barbarian and/or animal will show up. Right now I have 4 warriors and 1 scout, and 2 warriors is a minimal garrison. If I lose one en route, the new city is at risk from a lucky barb unit. Or, worst case, all the escorts could be killed and the settler lost. Sitting on a forested hill with two of the three attack vectors being across water is most likely to preserve my scant troops.
5. Building on one of the riverside grassland tiles means I can't farm that tile: 4F1C is almost as good as crab, and doesn't need a fishing boat, although I do have to invest 4 worker turns (and keep the worker safe while he's farming).
6. Building on flat land gives up the 25% hill bonus, which can mean the difference between keeping or losing the city. I'm trying to put most of my early cities on hills.

In favor of coastal build: coastal cities get extra trade routes from lighthouse and smuggler's port, and higher trade route yield from harbor. At that point the crab will be a 5F3C tile, quite good. Lots of investment to get there, though.

Overall, the hill defense bonus and prioritization of other techs over fishing are my strongest arguments for the hill plant.