Why are supports so good these days?

You are talking about games that are stomped. You saw recent game EG vs. Na'Vi.eu? 8:48 minutes gg from Na'Vi. Jakiro owned them (even though I am not talking about kills).

Supports are not good at carrying (getting kills - maybe except Lion and Lina), and they shouldn't. Ok, if there is a chance that a hero can escape, you should finish that enemy, but when I see that my carry will be able to get a kill on someone, I will let him do that (talking mostly about ganks).
When you see 22-4 Crystal Maiden you know that something went completely wrong.

Support's damage generally do not scale that well, maybe that's why you feel that early power of spells. It has to be at least decent in early-mid game to give any fun to supports :).

And again - getting good stats while playing supports does not make them late-game carries. Even underfarmed true carry on minute 50 should be able to deal with any support. If not, then it was a stomp.

Earthshaker Rampage? It can happen even if you have only Arcane Boots and Blink Dagger in 45 minutes.

Supports can kill, sure, but in even games they won't be that effective as you think.

But then you get the problem that not all cores are carries.
Its just a way of putting certain heroes in a role. No need to overcomplicate things by saying that a 20-0 crystal maiden is no longer a support but a carry.

Ive seen professional games that were really close, especially chinese, where for example chuan won the game for IG all by himself in 5 minutes with amazingly timed enchantress rotations, or really suprising arrows. All his teammates needed to do was play on their normal level and they rolled to victory all because of chuans perfect rotations in the first few minutes.
But i wouldnt use the word 'carried' do describe chuan in that game.

I think it's pretty clear that the "support vs carry" thingy is extremely oversimplified. There are more than 100 heroes in this game and you can't put everyone of them is either of just 2 categories. It's way more complex honestly.

For me it's a bit more relevant to see it this way :

- Farming heroes vs supporting/roaming heroes. This distinction only makes sense in the first 15 minutes of the game. Either you are assigned to farm a lane (either safe lane or mid), or you are assigned to either support a teammate in the safe lane or assigned to just roam the map looking for kills. Heroes with good early game kill potential (e.g Earth Spirit, Lion, Mirana, Vengeful Spirit) are good in roaming roles while item-dependent heroes with garbage early game but good mid-late game are good in farming roles.
Farmers get gold from creeps, roamers get gold from kills.

- Damage-dealers vs utility heroes. Either the point of your hero is to deal damage and get lots of kills, or the point of your hero is to provide utility to your team (e.g disables, initiation spells, buying utility items for the team, etc).

I prefer to look at it this way. For example Venomancer, Witch Doctor or Crystal Maiden are without question considered supports but they are definitely designed to be damage-dealers : that's the whole point of their ultimates. So going 25/2/10 with a CM or a WD doesn't surprise me at all.
On the other hand Enigma is definitely a farming hero but he's a utility hero : you don't pick him to deal damage but to farm utility items quickly (e.g mek, necrobook, sheep etc) and to provide disables for his team.

And the late game issue is something else completely, some supports have good late game and some don't, it's the same for carries. I'd choose a late game Enigma, Dark Seer or Silencer over a late game Viper or Wraith King anyday.

If you can win before the midgame really begins and deny the enemy team almost all exp and gold you can let supports carry. If it goes to lategame though and you didnt give your carry kills you will lose.