A brief review...
Apple purchased the N cards and included them in the Macs. Since they paid N card prices (as the hardware is N capable) they included the extra cost to them for an N card vs. a G card. Then, like any business, they passed this extra cost along to the consumer. You already paid for it.
The firmware update makes it so OS X can use the capabilities you already paid for.
You are not a very good businessman if you charge for your product based on your cost and not what the market can bear. Apple did not charge us for 'n' hardware. They shipped more than what was purchased, with the extra functionality disabled.
Apple is in a competitive market where price matters (ie, they are not a monopoly). 'n' hardware is more expensive than 'g' hardware. If they were charging for 'n' hardware and delivering 'g' performance, two factors come into play:
1. their price for a 'g' computer is too high. Fewer people buy.
2. they lower the price of the hardware to be in line with 'g' competitors. People buy, but per-unit profit is less than had they simply shipped the advertised 'g' hardware.
Either way, from an accounting perspective, Apple has lost the difference in price between 'n' and 'g' hardware (obvious in the second extreme; take the first extreme, and compare the profit there with Apple shipping 'g' hardware instead and you see the same is true in the first extreme as well).
You did not pay for 'n' hardware. You paid for 'g' hardware. Apple didn't 'lose' money on the overall computer sale, but they made less money than they should have been making were they shipping the advertised hardware instead of the 'n' hardware.
Again, posit the scenario where Apple shipped 'g' hardware with all those boxes instead. You would still have exactly what was advertised, still would have paid exactly the same price, still would have just as much company amongst Mac buyers, etc. Your behavior wouldn't have changed, because nothing you knew about changed. However, now, you'd be in a much worse position, having to replace your Airport Extreme card for $50-90 to get 'n', at best, or not able to get 'n' speeds without buying an additional external dongle or a whole new computer, at worst.
The ONLY argument that can be made is that you bought Mac boxes expecting 'n' hardware to be present, based on evidence presented on web sites. Which is a straw-thin argument, as (1) such web sites don't speak for Apple, (2) specific components can and do change throughout a manufacturing run so the fact that some people could see 'n' hardware in their box didn't mean you would get the same, and (3) the existence of hardware in a box does not imply the utilization of hardware.
So, you either bought 'g' hardware the best you knew, and are getting one hell of a deal to upgrade to 'n', or you took a risk acting on hearsay and rumor and it didn't pay off for you.