I suspect Ukraine was told quite clearly what they can expect, and as you say, it comes short of NATO boots on the ground, or wings in the sky.
I'd say no one ever really wants to defend an ally, it's more of a pros-and-cons balance. For smaller countries, solidarity within NATO is building goodwill capital for when they need help (e.g. with allies following US into Afghanistan). For large countries, this is part of their empire-building: showing allies you support them makes them more favourably disposed to you. All-around, even for the US, it raises the bar for anyone contemplating an attack on a NATO member.
Ukraine is a colleague but not an ally, so these don't really apply as much.
That said, the West wants an independent, pro-western Ukraine (just not enough to fight a direct war with Russia over), and seems unusually resolute, so I wouldn't be surprised if some truly punitive actions were to be taken. Exclusion from SWIFT was one proposal, interfering with Russian energy exports would be catastrophic for Russia. The latter is very difficult for Europe in winter, but who knows; the US could open the tap with their gas, also if the whole thing gets delayed by a few months, it could be a very different perspective.