It's OK data, but the average can be skewed high by some vastly inflated options that nobody cares about.
Most people will pick a ram spec and buy whatever is the cheapest kit for that spec at the time.
I think the best data view would be what is the cheapest available kit for each spec over time rather than the average price of each kit.
Wouldn't historical data also be inflated by the gold plated Monster branded RAM sticks too though? Making the now to then comparison, well, comparable.