People have a tendency of losing focus while striking - sort of a tunnel vision. They start focusing on their strikes and lose sight of their balance and posture. However, that's not the only flaw - lack of motion is another. Simply rooting will not be enough.
In the case of the sumo style pushing youmentioned - your base is under you, your center is lowered, and you are pushing your opponent away. It makes you hard to double leg. There are several other techniques you can successfully pull off, however.
i'm nobody...i'm nobody. i'm a tramp, a bum, a hobo... a boxcar and a jug of wine... but i'm a straight razor if you get to close to me.
-Charles Manson
I will punch, kick, choke, throw or joint manipulate any nationality equally without predjudice.
- Shonie Carter