Hulagirl, I think the problem is that what you are calling the mammalian dive reflex is not what you are describing - you're describing the involuntary cold water gasp reflex. Both happen as a reaction to cold water, but they're not the same process.

I don't swim really, but I know as a kayaker, we're all warned strongly about the cold water gasp reflex and the panic that it can cause, even if you're wearing a drysuit and should be fine in the water temperatures. The other thing to worry about is cold water getting in the ear canal really can do a number on your balance.

Links:
http://www.oregon.gov/OSMB/safety/co...mmersion.shtml
Four Stages of Cold Water Immersion

Stage 1 -Cold Water Shock
When someone falls into cold water their first unconscious response is to take a large breath of air, called the "involuntary gasp reflex." If their face is in the water when that gasp occurs, then their chances of survival immediately diminish.

http://www.ussartf.org/cold_water_survival.htm

I also find it funny that Hulagirl quoted a blog and Knotted yet is quoting scientific articles.