That's exactly it.
A crotchet is a quarter note. I suppose traditionally it's a quarter of a bar or measure in 4/4. Maybe that's why it's called a quarter note.
In 3/4 time you have three crotchets per bar, which is three 'quarter notes' per bar, except they're not anymore.
Time signatures make sense as fractions though, don't they?
4/4 = four quarter notes = 1
3/4 = three quarter notes = 3/4 of above. Each bar is 3/4 as long as a bar of 4/4.
4/2 = 4 half notes per bar = 2 Each bar is twice as long as a bar of 4/4.