Poor English of desis has less to do with which school they graduated from but where they started from. If your primary education was in Urdu Medium, you could pass through MBA in flying colors but you may have poor communication skills.
True. Spelling and Grammar has nothing to do with an MBA. You can do very well in a good MBA program and not be that great in spelling....but yeah it will hurt you once you go in the work force if you're not able to communicate in English properly. The work force for an MBA demands excellent interpersonal skills.