The reason you do to different decreases is that K2 tog is a right slanting decrease and SSK is a left slanting decrease.
If you don't do SSK (or do K2tog instead), your gussets won't match and they'll look strange on the one that should be SSK. :rollseyes: Once you get the hang of it, I think you'll like SSK. I really do.
Alternatively, you could do S1,k1,psso, or K2togtbl to get your gussets slanting the correct way, or check the decreases page under basic techniques to find another left slanting decrease that you feel more comfortable with.
Good Luck and Happy Knitting :XX: :XX:
P.S. If I got any of that wrong I'm sure Silver or rebecca will correct me.
They're the real SOCK GURUs.