"Because they squeezed RAM out of the N95 to hold it back like they did with 7650, they seem to deliberately spec phones to be out of date within 18 months"
A load of rubbish I'm afraid.
There's many serious problems with the theory:
-Many new S60 models actually have less free RAM than older models, so by your logic Nokia is actually discouraging us from buying new models. I'm currently reviewing the 6110, and it has half the free RAM of the N76, yet it's appeared in the shops after the N76.
-For the phones to go out of date the amount of RAM would have to increase over time, but it isn't increasing. It's hovered around the 20mb mark for the past couple of years. If you don't believe me, check out Steve's list of S60 device specs: http://3lib.ukonline.co.uk/s60history.htm You can verify these figures on the official Forum Nokia site.
-Why haven't they squeezed the N76 RAM?
"with more RAM the N95 would (ignoring build quality) last longer than that as it's pretty future proof otherwise."
Again, this just doesn't tally with reality. You're making out that each new generation of phones gets significantly more free RAM, but this isn't the case at all.
As for being future proof, there's far far more to a phone than RAM: network connectivity (wifi, wimax, HSDPA and future technologies etc), processor speed, operating system version, screen resolution, memory card size etc. All these things change over time, so even if you had a phone with a gigabyte of free RAM it would still go out of date unless you were just using it as a non-connected pocket computer.
Phone companies don't need to deliberately hold anything back, mobile technology is already volatile enough to encourage upgrades as fast as the manufacturers can get them out of the factories.
"All cynical marketing ploys, not as others have suggested, to save battery."
If it was a marketing ploy, Nokia would actually mention the free RAM somewhere in their marketing. But they don't, at all. Not on the official sites, not in the manuals, not on the advertising, not on the press releases, nowhere. I believe Steve or Rafe actually tried to ask a Nokia representative about this last year and the rep didn't really understand what free RAM was.
In fact until a few weeks ago there was absolutely NO official statement on how much RAM any of Nokia's devices had, not even on Forum Nokia. Trying to ask shop staff about RAM produced either blank looks or else the staff thought you meant the internal flash memory.
The only way anyone knew was through indendent technical sites that studied the phones, the kind of technical sites that 99.99% of customers would never ever read.
Here's another problem with your theory: very very very few people actually know what RAM is, let alone how much RAM their phone has, let alone care about it. It just isn't a selling point, most people never actually multitask with anything other than the phone's built-in applications.