I have been ezy cabin crew for nearly 7 years and I struggle to recount any instances at all where an order was abandoned because of insufficient change. If this was an issue, the airline would certainly do something about it; onboard sales are a very important revenue source.
Besides, we almost always manage to get all the change due by the end of the service. If that is not the case, a PA is made to pax to help out (I don't personally like the need for this intrusion, it definitely doesn't sound good and is less than great service). But as for lost sales, I doubt that's an issue.
By the way, I'm not defending any sides here, merely offering the explanation to ExXB's question.