Well, funny enough, if you look at the hacker news thread about Avatar hitting 1B, it is in fact discussed (one of the people mentioning it is me).
I stand by this, just as with movies: it matters. If not these numbers are completely arbitrary and meaningless. It is equivalent to comparing, numerically, the price of one company in Pesos vs the price of another in Dollars, it would make no sense unless they are both converted into the same unit. In this case, we don't even have to go that far back: even Microsoft's market cap in 1999 (adjusted for inflation) was more.
Oh, I kind of agree, but this just seems like "neener, neener, not the biggest."
To take a different angle, computers and electronics have only gotten cheaper since 1967. So maybe Apple should be compared to a deflation adjusted IBM market cap. How would those numbers stack up?
I think the main point is that any time value in a monetary unit is measured over time, it is naturally adjusted for inflation. This is done with basically everything. So it's not necessarily a "neener neener" situation, it's applying standard process.
I think the real question that is trying to be answered is which company is worth more, period. How do you measure worth? In dollars is one way, making use of the market cap. Which has/has made a larger (positive) impact in the world is another. Which metrics should you use to get to the answer is the question...
Adjusting for change of price in goods (your suggestion) is a little shaky of any idea in my mind, as 1. inflation affects all goods instead of a subset, which means there's more choice. 2. IBM must've had it harder since the cost was higher and they still managed such a large market cap, ie. took more value output to create the market cap.
I stand by this, just as with movies: it matters. If not these numbers are completely arbitrary and meaningless. It is equivalent to comparing, numerically, the price of one company in Pesos vs the price of another in Dollars, it would make no sense unless they are both converted into the same unit. In this case, we don't even have to go that far back: even Microsoft's market cap in 1999 (adjusted for inflation) was more.
Edit: link http://news.ycombinator.com/item?id=1079716