Why does for(x <- c; y = ...) yield {...} become c.map(x => (x, ...)).map((x,y) => {...})

I've been looking at http://docs.scala-lang.org/tutorials/FAQ/yield.html,
and found this

for(x <- c; y = ...) yield {...}

is translated into

c.map(x => (x, ...)).map((x,y) => {...})


This seems rather odd to me. Why not

for(x <- c; y = ...) yield {...}

is translated into

c.flatMap{ x => val y = ...; {...} }


Isn't this basically the same, but much more straightforward?

The reason I bumped into this is that I was trying to implement a bunch of
custom for-comprehension generators, and it kept asking for *.map*, and I
couldn't figure out why. These were pretty odd generators, e.g. a TryCatch
generator which you can put anywhere in your loop and which propagates a
Seq() back up if it catches an exception, and so don't really have
meaningful values to pass into *map* or *flatMap*s.

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