That's not exactly true, probably more so for LME than DME. If every batch of extract were the same it would be, but the unfortunate truth is barrel to barrel of extract doesn't have what the sugar content the producers actually claim. Homebrew stores that don't go through tons of extract may not realize this is true, and those that do don't want to admit it. It may be an average or in the ballpark but easily varies by 10% and more often than not is on the short side. 10% more water is 10% more profit.
But my opinion for the OP, stir it as I recommended. It will encourage the existing yeast to multiply. That's one reason why people use stir plates. Yes, they introduce some oxygen but the constant stirring makes the buds split off the parent cells, gets them out of the house and makes them get to work on scrounging for nutrients and making new buds themselves.
I would add more yeast based on what I am reading, but I don't really know what is going on. It's a guess based on answering the same question a few thousand times over a number of years and 3 decades of brewing.
Don't stir too much as to introduce oxygen at this point.
For the yeast strain you are using, temperatures in the 70's are fine... if you are somewhere where that is an option. Yeast propagates better at higher temperatures, (up to 90) but it becomes less than ideal for flavor.
... my edit follows...
A hydrometer is used before fermentation begins to establish the actual starting gravity. It also helps when new brewers ask for help with fermentation worries because it gives something scientific to go by vs a guess based on observation by untrained eyes. In this case it
seems you have micro bubbles indicating fermentation is actually occurring, just not at the rate you are hoping for.
You can look up the yeast strain you used on the manufactures website
http://www.whitelabs.com/yeast-bank/wlp530-abbey-ale-yeast
, and compare it to the recipe for suggested fermentation temperatures. I would guess you are a few degrees low... it means slower fermentation and less yeast contributed flavor. It's not a flaw to friends you may be sharing the beer with which may not appreciate the flavors created by that yeast strain if they are new to this style of beer.