: [BZZT!]

: No Balrogs ever fell to their deaths. Two balrogs, mortally wounded, FELL. Big difference.

That is a matter of personal opinion. I don't recall reading anywhere that the Balrogs which fought Glorfindel and Gandalf were mortally wounded. Besides, Balrogs were pretty tough characters: Gothmog continued to fight even after having his arm hacked off.

: And note that two winged dragons died after falling from the sky, because they, like the balrogs, were mortally wounded.

They were probably dead already before they fell from the sky.

: : ...And why didn't the Balrog of Moria use his wings when he
: : fell from the bridge and glide to a landing next to the
: : underground lake instead of plunging right into it?...

: For the same reason Gandalf didn't use his parachute-like cloak: the author didn't write it that way (and we don't know that it was a lake -- in fact, we have better reason to guess it was a river).

It is physically impossible to use a cloak as a parachute (or even as a glider). If such were the case, the Greeks would have been gliding since the days of Archimedes.

Regarding the lake, I will have to reread the passage, but for the purpose of discussion it is irrelevant - water is water.

: : ...Also, the fact that the battle between Gandalf and the
: : Balrog continued on the way down implies that they were both
: : falling at the same rate. If the Balrog had wings, why not
: : slow down and let the wizard fall past him?

: You're disregarding the fact that the Balrog had lashed at out Gandalf with its whip so as to drag him after it, and that Gandalf fought with the Balrog on the way down.

It could have simply been a desperation move - i.e., if I'm going down, you're going with me...

: Clearly battle, not sending him to his death, was what it had on its mind. And since Gandalf said they fell for a long time, it's a pretty good bet they didn't fall at a fast rate.

All objects fall at the same rate (unless acted upon by an outside force) which means that Gandalf and the Balrog were falling at the rate of 9.81 m/sec². If the fall took a long time, it was because it was one hell of a long fall; certainly long enough for them to have reached terminal velocity and shattered every bone in their bodies when they struck the water (which would have been as hard as concrete due to surface tension). The only reason I can think of that they were not pulverized is that they were both Maiar and capable of sustaining injuries which would have killed a lesser being - a weak argument at best.

Creative license is one thing, but I think Tolkien should have rethought this entire scene before submitting the final draft.

: (This all sounds so familiar....)

The Encyclopedia of Arda has a rather long and unbiased discussion concerning the subject of Balrog wings...
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Encyclopedia of Arda