1.) Over time, paid firmware update will decrease the price of the new server and/or its initial support contract. Rather than paying for "lifetime updates" the initial owner gets to pay only for his/her actual usage of updates.
2.) A functional post-warranty firmware market (with a culture where paying for this service was widely accepted) would mean more vendors would support their hardware for longer.
All completely wrong.
There are many vendors today who don't charge the premium prices that HP, Cisco, Dell, etc., charge, yet support their product for free for more than 5 years. I'm not talking about something that requires a physical replacement (i.e., warranty repair/replace), but rather firmware updates, posting new knowledge base articles, etc.
As an example, we just bought a Cisco computer with 4 processors (32 cores), 1.5TB of RAM and 16 900GB SAS drives. The price from Cisco was around $120K, while buying that exact same hardware (reference motherboard from Intel, Seagate drives, Crucial RAM, LSI RAID cards, etc.) as a "white box" would cost around $40K. Since the individual components will have the exact same warranty that Cisco gives (more, in some cases, like the RAM), what, exactly does that extra $80K buy? And, how much do you think they will lower their price if they only have to produce firmware updates after the three-year warranty expires for people who pay for extended support?
Basically, the only way to get extra sales by not providing support is for these companies to slash the initial sales prices in half, and that's never going to happen. You might see a 5% drop, but knowing that you'll have to spend even more that than for the support, you'll go elsewhere.