But that doesn't make sense. Communications signals come in on subspace carrier waves and if they couldn't detect them they'd never receive any messages.
So it does make sense after all? I mean, I just argued that subspace carrier waves are consistently detectable and this is because they are a long-duration phenomenon.
How does Nero get the drop on 47 Klingon ships?
He can kill a planet with, indeed, a drop. Catching a Klingon frontline garrison world by surprise would be a nice way to accomplish such a trick... There'd be no opposition afterwards, but OTOH a space detonation of red matter would leave planetside witnesses to spread the message of terror to Starfleet, thereby leaving Vulcan defenseless.
But if Nero really uses this as a ruse to get Starfleet away from Vulcan, then surely the battle site must be distant from Vulcan - while Nero himself has a slow ship... Which is why I still prefer the idea that there was no battle, merely a false message that indicated a horrible threat approaching from the direction of Laurentius which is nowhere near Vulcan or Nero's previous location.
That's probably the weakest approach, as starships have energy and power to burn. Escaping a planet is an established feat - starships even escape black holes in TOS and VOY! Towing
a planet is a feat not yet established, but it should not be all that far beyond the capabilities of a single ship; Spock and Picard come close to achieving it in "Paradise Syndrome" and "Deja Q", respectively.
Whether starships move by using thrust is far from established. We have never heard of a "rocket blast" associated with impulse power, and indeed starships themselves appear immune to such things, as impulse engines often are facing starship structures without frying them. Perhaps impulse drive is purely gravity manipulation (that is, subspace trickery, as subspace fields remove inertia)? Even if it's not, Starfleet has gravity tech, and could direct the ship's power to gravitic landing and takeoff engines if need be.
...But nowhere the size of a Borg ship yet. And bigger things have lifted off planets in Star Trek...
The energy requirement to escape and in fact manoeuvre rather effectively and speedily within an atmosphere have nothing to do with real world physics any more.
Why is this a problem? Real world physics could not explain how the Enterprise
got from Elas to Troyius in such a short time, let alone how she got to the Tellun system in the first place. Propulsion in Trek is fundamentally and consistently immune to currently known laws of physics.
That doesn't make it ill-conceived or contradictory, though. Not unless for some reason starships were unable to land on planets and lift off from them!
Now they can zip around in a planet's gravity like a TIE fighter.
If by "now" you mean "Tomorrow is Yesterday"...