It's not always easy to talk about trust and reciprocity. Many standard assumptions about them assume a rubber-and-glue relationship: your trust bounces off my reciprocity and sticks to you. That is, if I trust you and you prove trustworthy, then I'll trust you more next time. Similarly, if I distrust you and you reciprocate in kind, I will continue to distrust you in the future. Or so goes the assumption. Weirdly, many experiments find glaring exceptions to these predictions. Weirder still, anomalous results are only seldom presented as such. They're usually found in footnotes or an appendix. If you ask me, the apparent unruliness of reciprocity in lab settings is one of the most remarkable discoveries on experimental economics since Berg, Dickhaut and McCabe ran the first trust games in 1995.
If, as I secretly suspect and as the experimental results sort of hint at, trust and reciprocity are more orthogonal than they seem at first blush, and it's true that a prosperous anonymous, impersonal economy needs an admixture of both, then we should expect to find institutions that bolster both.
Gift-giving on holidays encourages reciprocity. The Dub-MOE doesn't mention it in his famous Forbes article, but perhaps the reason the institution of regularly giving in-kind gifts persists is that this institution exists as a bulwark against alienation.
Gift-giving might not be individually euvoluntary: I am softly coerced by my need to maintain good relationships with loved ones to buy them more or less thoughtful presents on Christmas and birthdays. Individually euvoluntary or not, gifts are almost definitely meta-euvoluntary: I strongly prefer to live and conduct my affairs in a society with high levels of reciprocity and if the price for that is that I have to brave the thicket of humanity in a Target in December, that's a cheap price to pay.