Bad power presents an amp company with two choices... allow the amp to operate but put it at risk of damage and failure or protect the amp from damage by shutting down the power supply.
With customer expectation for reliability being as high as it is these days, and the expactation for longer warranties than offered in past times (remember the good 'ol days of the 90 day or 1 year warranty that was non-transferrable?), the customer has pretty clearly voted that having the amp not fail or blow up or let it's magic smoke out is preferable to one that might work in some adverse power situations but then fails.
We spend lot of effort towards long term reliability, as many of our products are used for professional and international touring applications. In these applications, power is generally pretty good (typically fewer issues than the backwoods club circuit) but long term reliability, especially after hundres of thousands of traveling miles, is of prime importance. The last thing one of these users wants is to have an amp fail due to bad power, so the protection is focused towards long term reliability on the road.