Do you really want to spend at least $1200 just for a the remote possibility that that model might support 2GB more than the 2.4GHz model?
I honestly don't know what Apple is up to with the hidden upgrade. But Crucial doesn't even mention the 2.66 and 2.93 models on its website (I assume it's because they are already equipped with 4GB) and OWC says they can only work reliably with up to 6GB. Now why would the two companies not want to cater to those crazy enough to pay $700-$1200 for 2 sticks of 4GB?
And as far as the Apple online store is concerned, you should at least point out that you can't access the memory upgrade directly, nor does Apple claim on its website that any of the MBP 15-inch versions currently support more than 4GB:
"Processor and memory
15-inch MacBook Pro
2.4GHz Intel Core 2 Duo processor with 3MB on-chip shared L2 cache running 1:1 with processor speed; or 2.66GHz or 2.93GHz Intel Core 2 Duo processor with 6MB shared L2 cache
1066MHz frontside bus
2GB (two 1GB SO-DIMMs) or 4GB (two 2GB SO-DIMMs) of 1066MHz DDR3 SDRAM; two SO-DIMM slots
support up to 4GB"
http://www.apple.com/macbookpro/specs.html
I think that there will eventually be a firmware update for all Unibody MB/MBP models. After all, they are all equipped with the same NVidia chipset. It just doesn't make sense that Apple would screw over all the buyers who paid extra for the 2.53Ghz and 2.8Ghz models at the time. Is there a precedence for that?
I think with Snow Leopard and the price of 4MB modules coming down, Apple will patch the systems that have the older firmware.