Downtime costs him. So much so that he's willing to pay for uptime.
Also, it didn't cost him "nothing". He paid for service. It wasn't free.
Your reply sounds like you don't value him as a customer anymore because he's not giving you money anymore. Nobody forced textdrive into offering the "lifetime" package. You should treat him like a valued old customer, rather than calling his logic "interesting".
I think you mean: replies.
Wait, what? Who owns and operates the servers?
I completely understand that he's 'getting a great deal', and that he isn't currently paying you anything, and that he may well have lasted as a customer longer than you expected, but your company offered lifetime service for a fixed cost, and he bought it. As I understand it, this was to bootstrap your later efforts.
To constantly demean his position is as insulting to him as it is to your integrity. While you may feel like you're in the right here, I can guarantee that you've lost at least one potential customer, because I will not be using Joyent. I'm guessing that running potential customers away isn't your intent here so please, don't do yourself any further harm.
The packing system is the same, it's BSD userland. The paths are the same. Everything is the same. The kernel shouldn't matter. And if you had told support that you wanted us to just migrate you because nothing was out of the ordinary, what would they have done? They would have migrated you ....
And this has been quite a good deal for you. The logic of moving from something that costs you nothing to something that does costs you something is interesting.