HawkinsT said:
So why not just use a clear filter to be safe?
Cheap ones noticeably degrade image quality and often make a lens far more prone to flare... mid range ones do this too, but to a lesser (but still noticeable) degree - if you're using them with cheap lenses, fine (although I would rather just risk having to buy a new lens), and if you're using them with expensive lenses, you are loosing a lot of the quality you've paid extra for. The more expensive filters, such as those by B+W, are fairly good and don't tend to introduce any noticeable change in image quality, but then you're spending £70 on a filter to protect against a very unlikely scenario you're most likely insured for already.
The main reasons I use filters are two-fold. First, they are required for weather sealing of some lenses, and beneficial for weather sealing in other lenses. Second, they are easier to clean than most front elements (except the newest Canon lenses with the fluorine coating), and if I need to clean the filter in a hurry (usually following a water splash) and there's a bit of grit, the easily replaceable filter gets scratched, not the front element.
Regarding insurance, that can be a sticky issue. Yes, all my gear is insured. But at least in the US (not sure if it's the case elsewhere), it's a common and very cost-effective for non-professional shooters to get insurance from their homeowner's/renter's insurer, as a separate policy or a rider. The problem there is that any claims against the policy are reported to the CLUE database, which is used to determine rates and eligibility for the primary policy. So, despite having no deductible, if you make a few claims for damaged lenses you may find yourself paying more for your home coverage, or being denied coverage entirely. So, personally I view insurance as coverage for major loss - if I damage a lens that Canon will charge me $400 to replace, or my EOS M drops to the ground and shatters, I'll cover the repair/replacement myself. If someone steals my 1D X and 600/4L IS II from the back of my car, I'll file a claim.