You could take this a step further, though. For most activated abilities, the activation occurs and the ability goes to the stack. In general, you can't target mana abilities the way you can target other abilities because mana abilities do not use
the stack. The reminder text is generally added to help the players, but it isn't really necessary.
Detain, on the other hand, doesn't target the ability; it targets the permanent. So what we're talking about now is a static ability applied to the permanent that lasts until the end of the turn that prevents
activation before it can even start. That's the distinction: spells like Stifle
counter the ability after it's activated and while it is on the stack, but they can't stop the activation itself. Detain stops the activation before it can happen.
As far as I know, the only card in the game that stops activations before they happen but still
allows for mana abilities is Abeyance
. In that card's case, it was quickly errata'd back in the 90s to ensure that it wouldn't become a white Time Walk
. It's strange that, when the power level errata's went away (and Time Vault
started getting ridiculous again) and they started making the oracle wording as close to the actual wording as possible, The oracle text for Abeyance wasn't change to become more consistent with things like Detain or cards like Null Rod
. It almost seems like an oversight on their part that keeps Abeyance from acting just like Null Rod on, say, a Sol Ring