I think they're more hedging their bets on customers using the service for a few months and replacing their current (if they have it) host with Linode and once their credit runs out being so invested in Linode as a service -- realising it rocks and having their stuff all there -- they won't have a reason to move and if they choose to it'll be a pain to do so.
True, but if they extended the deal to current customers they'd still have the same outlay ($100,000) but the buzz + new signups would be increased.
I suppose it could be argued that current customers are more likely to sign-up for a second linode independently from any offer; but in counter to that, some current customers might be dissuaded from signing up for a second linode in the near future because the perceived value proposition has been lessened.
I think allowing current customers to sign up for a 2nd linode would be a win-win for Linode (and people like me who currently use them).
