According to Apple, alcohol should not be used on an iPad. iPads have an oleophobic coating for repelling oil. Each application of alcohol will cause significant degradation of the oleophobic coating. For more information, see: http://support.apple.com/kb/ht3226

likely dangerous for most android phones too, alcohol could stain/cloud plastic screens.

iPhones have the same coating as well. Maybe the "grime" this person noticed on the cleaning pad was the coating!