Yeah.. 1-2.5lbs a week is definitely NOT a plateau! It's just that you're getting closer to your ideal weight and your body can't reach as large of a calorie deficit. Also, as we get closer to our ideal weights our bodies are more and more reluctant to give up the extra weight.
FWIW, I lose on a scale of more like 2lbs/month (sometimes up to 4/bs, sometimes none at all) so your weight loss sounds absolutely speed to me!
Oh... and I was both 175lbs and 185lbs for quite a while before this journey and never had that issue. It did take a bit of time to reach 175lbs BUT that has more to do with my cycle (I hit 175lbs before TOM and then I often have to wait until after I ovulate to loose again). After reaching 175lbs I barely even saw it because I dropped a few other pounds in quick succession. Our bodies don't lose in a nice, neat linear pattern because there are just too many factors going on in our bodies that contribute to the number that we see on the scale.
The weights I did get stuck at for longer periods of time (190lbs, 169lbs) were not weights that I had ever been for any significant amount of time before this journey and both made sense (the first I started weight lifting then and the second I took a mini-maintenance break for the holidays and I think I was retaining water for awhile afterwards too).
"Sticking" Weight
I've been losing pretty regularly since beginning the program in August, but it has slowed wwwaaaayyyy down when I hit the 180s... (50 pounds lost!) I went from 3-4 pounds per week to 1-2.5 pounds. I know I should be grateful for those pounds, but I don't know if it is considered a plateau when you're actually losing?
It has taken me 6 months to lose 50lbs...whereas there are others that obviously lose much faster. We are all different 
