dstiles - 9:31 pm on Nov 30, 2012 (gmt 0)
The answer is in the hands of the IT people for the companies concerned. If they state in their DNS records the purpose of a specific IP range they will gain more respect and fewer complaints. Very few hosting companies do this; I've mostly seen it noted by DSL providers.
To give them their due, Amazon does at least state in their DNS records that ranges are used for dynamic (cloud) hosting.