The MacBook Pro 2008 issue with NVidia 8600M was recognized a lot quicker because NVidia did recognize and provide a fix quickly.
Apple never issue a replacement program until they have fully diagnosed the root cause of the issue and have a fix for it.
Another similar example that took a lot longer than for the MacBook Pro 2008 case, is the iBook G3 800MHz which have exact same symptoms as we have here with its GPU (which was an ATI Radeon 7500).
In that case, Apple didn't issue a replacement program quickly, it took 2 or 3 years for it to happen. But they did issue a replacement program and developed a fixed logic board. I still have this machine which is now about 10 years old and it still works perfectly even though it has been repaired twice for the GPU issue, first time with a not fixed logic board (which explained why I had to get it repaired again), second time with the fixed version of the logic board, and since then the issue never appeared again and the machine is still working perfectly today even though it's almost 10 years old.
So it is certain that Apple will issue a replacement program, if this issue is not just a production issue on some batches. But it'll not be done until the root cause has been identified and a fix has been developed.
And considering that the amount of cases has increased only since August/September 2013 (see survey that show that very clearly), before that date the amount of machine being repair for this issue was still within normal level of repairs for a laptop, and so Apple probably didn't start to investigate on this issue until very recently.
From my point of view, the delay is still within usual delay for similar issues (the NVidia 8600M issue can't really be considered similar as it was widespread including in the PC world and NVidia did recognize a defect on this chip. The current issue is more comparable to the iBook G3 800MHz GPU issue I mentioned above that's to say apparently specific to these machines (no similar cases on the PC world) and no defect officially recognized by the GPU maker).
The more important here is not how old are these units, but since when the number of cases of this issue as significantly increased. And that number increased only very recently, that's why there is no replacement program yet as Apple didn't finish investigating (and in fact started to investigate on it only very recently) on it and don't have a fix yet.
And for having witnessed several replacement program policy in the past with Apple I can tell you that:
1. Apple,never publicly communicate on an issue (even at the Genius Bar) until they have fully identified the root cause. Before that they just replace the defective part.
2. Apple never issue a replacement program until they have found a fix.
And considering that this issue only significantly increased very recently, I think that neither of these two points are verified yet.