This loft has a lot of exposure but doesn't an owner stand risk of losing all that natural light with each of the three buildings adjacent to it having FAR of at least 10 floors?

Yes. All those windows facing east are on the lot line, and should be so marked on the floor plan.

(1) What's "FAR", and (2) how can you tell from the SE listing that the east windows are on the lot line?

FAR is "Floor Area Ratio", or how many square feet of building can go on a given lot. There're lots of other constraints: http://www.nyc.gov/html/dcp/html/zone/glossary.shtml

The SE listing itself doesn't tell you which walls, and therefore which windows, are on the lot line. You have to look at the aerial Google view of the building.

That may not be clear, either. E.g., I have two windows on the lot line, but the building next door has a side yard of maybe 10'. That building is 15 floors and uses its full FAR, so is very unlikely to be razed and replaced with something using the side yard. Those two windows of mine are still considered lot-line, though, so need to be of more fire-resisting construction than the others.

That drawing in the glossary explained it well. Thanks for the link.