Tinefol has the right idea.
1 and 2 I definitely agree on (although one is so hard to determine for sure, he'd have to have missed a land drop already). I would consider 3 to be just on part of a larger group of strange-situations-where-it's-ok-to-counter-Top.
So yeah, say your opponent has a fetchland out, three other lands, no cards in hand, and then he taps out his non-fetches to play Goyf and Top, obviously you spell pierce the top.
Or like your hand is loaded with heavy spells but no land disruption, so you want to get rid of cards like Spell Pierce and know you won't be open to cast it for a while regardless of what you're afraid of. I can think of other exceptions, but you'll probably notice them in the course of the game.
The point is that you'll need some outside justification to even Spell Pierce a Top, and a very, very good reason to use a Force of Will.
Possibly it's a difference with UW Tempo generally putting them under mana pressure, but I think it's just a misevaluation of the relative effectiveness of cards. When I look over a list like NO Bant or CB Bant, I don't see very many cards that stand out as something that they're looking for. It's all the same reasonably useful cards. It's not like they can look for Ancestral Recall or something and that digging to power cards is worth a card and a bunch of mana.
Since all the cards are basically the same (Goyf vs. Lifelink Goyf, etc. it doesn't matter, you'd rather just draw one without wasting extra mana) the only real choice that Top gives you is you get to pick whether you want a land or non-land. That sounds extremely powerful, but in practice you never get that choice.
But using Top the way it "should be" used is predicated on drawing multiple fetchlands to shuffle away the cards you don't want.
That means you don't GET to pick non-land (at least not for long -- you end up having to pick about the same ratio as land/non-land that you would have gotten anyway, meaning that top was useless) and if you want to pick land because you're mana screwed or whatever, it costs you mana to pick land and then you need to luck into the land to keep using it to get more land.
