While I'm agree with you that credits must be given where it is due, stretching it to the fact that this behavior would be in their DNA seems not backed up by facts in my point of view.
Do the down-mods represent people operating in good faith thinking I'm being mean-spirited, rude, and damaging the conversation? Or are they Apple fanboys upset by a little uncomfortable teasing at their expense? I can only speculate. :P
He is probably getting downvoted by people who
1) don't see it as sarcastic
2) Think it detracts from the conversation and encourages behavior of a similar sort.
This is great for OSM because it's starting to show how it's a real player, not just as as "open source map data", but "map data", i.e. it's competiting with the big, non-open source, map data providers now.
And think about it, everyone who they'd want to know that it is OSM, now knows :-P
April 2010 is around when they would have started working on the maps back-end. Attribution would have meant dev releases would have indicated Apple using non-Google Maps data. They probably wanted to avoid that.
Some of the comments were implying that Apple didn't give credit because they have a culture that is insolent. I was just trying to give context to the decision.