I'd find a calendar that lists only Federal holidays to be fairly useless. It just doesn't give me all the information I want. Federal holidays are useful for knowing when snail mail will be delivered, when a phone call to IRS won't reach a human being, when employees will expect to be off, and when banks will be closed, but life is a bit more complex than that. Hell, the US Federal Holidays list doesn't include Election Day or Tax Day, because as important as they are, they're not days off for government workers (or most anyone else). Apple's calendar includes Election Day, Tax Day, and even Flag Day (for the really jingoistic among us). Mothers Day and Fathers Day don't show up on the Federal list, but woe unto the child or spouse that misses either. Valentine's Day, St. Patrick's Day, and Halloween, though religious in origin, are effectively secular holidays that are too widely observed to be ignored.
I'm not religious, but I like having a calendar that lists religious holidays, because those holiday observances impact my business, social, and family interactions. Should I suggest an afternoon beer bash on Easter Sunday, or a business lunch with an observant Jewish or Muslim associate on fast days like Yom Kippur or the entire month of Ramadan? I think it's better to avoid such faux pas. For that matter, although I'm not the type to send greeting cards at the drop of a hat, there are those who do. Again, it's nice to know when such an occasion approaches.
That said, another approach for Apple would be to offer multiple calendars. US Federal Holidays, US Secular Observances. US Christian Holidays, US Muslim Holidays, US Jewish Holidays... The only downside is that all that granularity would make the Calendars list a good bit longer.
Apple's US Holidays list has 45 dates on it. Google's has fewer. If you have a Gmail account, use Google's if you prefer. Google's includes Black Friday (gotta keep their advertisers happy), Apple's does not. Apple's has Veteran's Day (November 11, WWI's Armistice Day) as well as its Federal observance (the preceding Friday if the 11th is a Saturday, or the following Monday, if the 11th is a Sunday), Google's has just the Federal observance. On the religious side of things, I'll skip the oft-criticized non-Christian holidays and note that Apple's calendar includes Palm Sunday and Orthodox Easter, Google's does not. Neither lists Ash Wednesday... Google's is clearly superior for those who don't want to see non-Christian holidays - there are zero, not even the most commonly recognized Jewish holidays.
Regardless, it's highly unlikely that any one ready-made calendar will be perfect for a person's needs. They are simply conveniences, and we're expected to customize and personalize them. That's far easier to do with electronic calendars than printed calendars, so all this quibbling about a calendar that can be either used or banished with a click of the mouse seems pretty silly.