Guppies are tropical fish (found in the wild in tropical or warm environments) They need to be kept in a warm environment to thrive.
To put it simply, if their environment is too cold, they have no biological way of "warming themselves", and will eventually die.

The reason why things do slow down for some fish at lower temperatures, is because more energy is spent trying to keep warm, that could be used for growth or reproduction.

As far as Woolworth's goes, did you mean they are everywhere in the history books, or something else?

Lastly, I seem to remember someone posting in to this site a while back who refered to themselves as a guppy noobie.  Was that you?

Have you considered getting a heater for your guppies?  Maybe you could move them into a warmer location in your house.  I think you'd all be happier.