Oh, come on. Get real. The world TCP speed record is 10GE right now, it'll go higher as soon as there are higher interface speeds to be had.
You can buy 100G right now. I also believe there are some 40G available, too. Also, check this: http://media.caltech.edu/press_releases/13216 That was in 2008.
I can easily get 100 megabit/s long-distance between two linux boxes without tweaking the settings much.
Until you drop a packet. I can get 100 Megabits/sec with UDP without tweaking it at all. Getting 100Meg/sec San Francisco to London is a challenge over a typical Internet path (i.e. not a dedicated leased path).
Or they might tweak some other TCP settings and get 30 meg/s with existing 1500 MTU. It's WAY easier to tweak existing TCP than trying to get the whole network to go to a higher MTU. We do 4470 internally and on peering links where the other end agrees, but getting it to work all the way to the end customer isn't really easy.
I guess you didn't read the links earlier. It has nothing to do with stack tweaks. The moment you lose a single packet, you are toast. And there is a limit to how much you can buffer because at some point it becomes difficult to locate a packet to resend. *If* you have a perfect path, sure, but that is generally not available, particularly to APAC.
But in a transition some end systems will have 9000 MTU and some parts of the network will have smaller, so then you get problems.
Which is no different than end systems that have 9000 today. A lot of networks run jumbo frames internally now. Maybe a lot more than you realize. When you are using NFS and iSCSI and other things like database queries that return large output, large MTUs save you a lot of packets. NFS reads in 8K chunks, that can easily fit in a 9000 byte packets. It is more common in enterprise and academic networks that you might be aware.