As a general rule, yes. There are probably a few exceptions to that rule (Mid-Ohio?), but it's simple supply and demand for most tracks. There are a lot fewer riders who will take off work mid-week to ride, so the price drops.
Also watch that you're not expected the multi-day discount on a single day. If you book any 2 days back-to-back, the second day is $10 cheaper. So if you book the same track later, but only 1 day, it's going to look like it's more; when in reality, you just got a discount the first time around.