I believe the phrase is idiomatic, and the expression simply means "as expected," or "as can be reasonably expected." A synonym would be unsurprisingly, while a similar idiom would be "it's no surprise that..."
As you might expect, typically the bigger the overall operating budget, the higher the average salary.
The class description starts out with the word class, as you might expect, and the name of the class.
As you might expect, someone who has had just one or two late payments typically looks better to lenders than someone who has had a dozen.
One book mention that the phrase can help put two people "on the same side of the fence":
Helpful Phrase #1: “As you might expect”
This little gem suggests that you and your customer share a worldview. It puts you both on the same side of the fence. It also allows you to share information with the customber, while suggesting "I know that you already know this."
I think might gets used in this phrase because it sounds more polite and less presumptuous than, say, "As you would surely expect." For all practical purposes, that phrase would pretty much mean the same thing, but might is gentler, and allows for the possibility that the other person might actually be surprised instead.