Insurance is a business, and it must be profitable otherwise companies wouldn't be in this business. That means that, on average, an insurance company takes in $y a year from premiums and pays out $z a year in claims where y > z. In other words, if I take my premium and put it in a bank account every month, changes are over time I'll have amassed more than the replacement cost of my phone. Yes, some people make out on insurance but others pay premiums and get nothing back. The only people guaranteed to make money off insurance are the insurance companies and those who put themselves at risk for being sued for insurance fraud.
Insurance is great for some things. If my house burns down I wouldn't be able to afford to rebuild it. If I get diagnosed with some horrible disease I'm glad I've got health insurance. But if I need to shell out $500 for a new phone if I do something stupid and break/lose mine that's not going to break the bank. And if it would break the bank, I'd have to strongly consider whether I need a DroidX or if it would be better for me to look at a lower-end phone. Over the past way too many years I've never needed to replace a phone for reasons other than obsolescence or boredom, for me insurance just doesn't pay off.