A lot of the achievements are included as references to popular culture or history, or just because there was an opportunity to use a cool name: From Russia With Love, The Last Crusade, Longest Name Ever, He Threw a Car At My Head, Capture of Brielle, Apocalypse Now, Greek Fire, the list goes on... They're there for fun, for those players that get the references (like My Little Pony, which I had to have explained to me since I was ignorant of Catherine's supposed *ahem* interests!), not as a measure of how well you are doing at the game.
These are the sorts of achievements that you're pretty much never going to get unless you set out to get them deliberately - not because they're hard, but because they're so specific. I think it's tough to get far beyond 50% of the achievements unless you're shooting for them specifically or you play all the scenarios as all factions, all map sizes and on all difficulty levels. In other words, hours don't much come into it; it's whether you spend a significant proportion of those hours chasing achievements or not.