Top of the screen not working, digitizer or motherboard?

Early last year my Ipad was dropped an it cracked the screen. I took it in to a local repair shop and they replaced the glass. At that time I purchased a warranty. Last week the Ipad was dropped again causing another cracked screen. When I picked it up I noticed the top half of the screen was not responding to touch. They told me the unresponsive touchscreen was due to some damage to the motherboard and there is nothing they can do. They did offer to replace they Ipad under the terms of the warranty for an additional $200.

I am by no means and expert, but I would think that this is a digitizer problem (which is covered under the warranty) not damage to the motherboard.

Thanks for any help.

James