EOL on V5R4 was not 1/27/2009. That was announced end of Marketing.
Meaning you weren't supposed to be able to buy new copies of V5R4 for your
new system, nor get support upgrading to V5R4 from an earlier release
before then. I think they extended that out to 5/27/2011. End of support
isn't until end of September 2013. Then again, your definition of EOL and
mine might differ.
I recently heard of people saying they were only upgrading to 6.1 because
they're vendor doesn't support 7.1, yet, after two plus years of general
availability. Love to know who those vendors are. You also had a good
question about are there vendors who do not support 6.1 yet. You can spot
those who are killing off their i accounts.
It took a long time for Trend Micro to support Scan Mail for Lotus Domino
on IBM i 7.1.
And nothing nauseates me more than a vendor who thumps their chest and
brags they support back to V3R2 but can't support the current release
until a couple of years after GA.