The major problem with your analogy is that storefront windows don't have hundred or thousands of bricks thrown at them everyday. Web hosts are basically under constant attack. Would you suggest that the CIA, NSA, etc. not worry too much about their computer security? If not, then I don't see why you would imply a web host shouldn't be expected to secure their servers as much as possible either.

If a storefront was under constant attack, then yes, they should have bars over it. In fact, in my hometown, there was a streak of vandalisms where kids were throwing bricks through windows. After getting hit 3 times, one store replaced their huge glass windows with smaller plexiglass ones.