BobG said:
Romney's not the only politician that hasn't fully encompassed new technology (George Allen comes to mind), but is it actually possible today for a politician to talk solely to a small group of people?
Yes, of course it is. The defining feature of "a small group of people" is
security, and that's where Romney (his staff) failed here. But this is one of hundreds of similar appearances Romney (and Obama) made that was supposed to be behind closed doors, in front of a friendly crowd. All the rest apparently were, but this one wasn't.
Certainly, they must always weigh the risk that there might be an infiltrator in the meeting, but I don't think the risk is really all that high, given the high pricetag for attending.
A candidate should assume that anything they say in any sort of public or semi-public environment is going to be presented to the entire public. There is no such thing anymore as a private dinner for donors...
That's certainly safe, but I don't think it is reasonable or realistic. It applies even more to open-mic gaffes, but there have been a lot more failures on that front: if there is a mic in front of you, assume it is on. Most politicians, including Obama, have violated that thumb rule.
(and, to be honest, providing the "secret" scoop to donors while saying something completely different to the general populace probably decreases a candidate's credibility even among donors).

Giving a different tone/spin/message to different audiences is a critical social skill and reality of life for everyone, not just politicians. Do you not talk and act differently in front of your family and friends than you do at work? Obama's Russia gaffe was a similar issue:
if he hadn't had an open mic in front of him, the statement would have been fine, but it was a statement made for a specific audience that wasn't appropriate for broader audiences.
And
of course donors want "the secret scoop"! Why else are they there? This question/answer in particular was exactly the kind of thing I would expect: frank discussion of the strategy behind the public face of the campaign, not just the mindless talking points the public gets. Politicians are in a position when running for office that all but forces them to talk out of both sides of their face. They all do it. But a high rolling donor is going to want the clear truth.
Consider how Obama might have had to deal with a question on gay marriage in 2008, in a high roller donor meeting. In a room full of liberals, he can't say he's against gay marriage, particularly if he really isn't. He'd have to tell them the truth if he wants their money, which, as I understand it, was that he was against it because he felt he had to compromise his principles on that issue to get elected. Romney would probably say something similar regarding his healthcare stance from his governorship. High roller donors aren't idiots: they know how political campaigns work -- they're neck deep in them!