Terrorist Math: 3+1=4

I noticed a strange coincidence with 9/11 and the London bombings, although what it means I don't know for sure-- I think maybe it is some sort of signature to show these acts were done by the same people.

On 9/11, 4 planes were hijacked, 3 hit buildings, 1 didn't-- this 1 plane crashed on the ground, and much later than the first 3 planes.

On 7/7, 4 mass transit vehicles were bombed, 3 subway trains (inside the ground), 1 bus above ground-- and this bus was bombed much later than the 3 trains.

Is this all just a coincidence?

It is hard to believe it is.