I've had the pleasure of performing at least 5 inspections in the last 6 months for homebuyers after the home had already been inspected by another home inspector.  Why is it that on all 5 inspections I was the first to clear out the cobwebs and make footsteps in the loose blown insulation???  All 5 attics were not the type that you could see everything from the access hatch.  I had a Structural Engineer tell me the other day that I was the only inspector he was aware of that walks attics in the Omaha Metro. 

I can't tell you how many attics I've found excess moisture on the roof deck, cracked rafters, sagging rafters, ridge supports not secured, cracked purlins, windwashing, inadequate attic ventilation, flex supply ducts entirely disconnected, spliced wires (some burnt), lots of damaged attic trusses, roof leaks, insulation issues, etc.

It's crucial to walk an attic for your clients.  The only time I don't is when I can't physicall fit...and I'm not 300lbs;-)

If a home inspector isn't walking the attics, it's a disservice to his clients and someday it'll come back to bite them.