It would make no sense for them to remove the entire page when they could just remove the Starbucks logo, so it could ell just be a restructuring of the site.
I don't think it's unreasonable that they'd have responded by deleting the page, though. It's the fastest and easiest option, (perhaps the website admin isn't available) and excising the Starbucks logo alone would look awfully suspicious. Seems like exactly the thing someone would do on the spur of the moment during an "oh shit" moment when they realized a viral marketing campaign might be compromised.
In this case, you've got multiple people sharing what should be an individual account and the potential for damaging mainstream media stories if people feel like they're doing a good turn for strangers, only to have scammers empty the card. Not to mention that if Jonathan's Card is genuinely unconnected to Starbucks, his use of their trademarks would make the lawyers uncomfortable.
This may not be a full-fledged viral marketing campaign, but I'm skeptical that Starbucks would be so enthusiastic about it if the guy responsible didn't have a preexisting relationship with their marketing department.
Somebody who loves your company showing initiative and doing something interesting that creates headlines for your brand? And you're not paying the tens/hundreds of thousands that it would have cost to get some firm to think of this idea? Hell yes we'll take that.