Re: techniquies in street fights
In the ' real world' you could expect to expect the unexpected, an attacker could and probably would attack in any way. Grabbing before punching is common, as is bottling etc etc. it depends on the situation, environment and the aggressor.
It is pretty doubtful someone would attack you with a perfect shomen uchi, but that is not to say that shomen uchi is a weak strike. I myself have broken someones nose with this strike (not something im proud of btw) and i've also seen another aikidoka's nose get broken with shomen uchi. If delivered correctly it can be a very poweful strike, the knife edge of the hand is particularly suited to striking (see armed and special forces hand to hand techniques) and is less likely to result in the striker getting hurt e.g. a broken knuckle, fingers or lacerations.