R eaders email me almost every week asking wheth er it's a good idea to purchase a home service contract, com monly known as a home warranty.  As with any so-called extended warranty, my answer is that it's probably better to self insure by putting the roughly $200 to $800 you'd spend annually into a savings account or dedicated product repair and replacement fund. And I'm not the only one who feels this way. The non-profit Consumers' Checkbook gives the same advice in its home warranty coverage. Admittedly, home warranties have an edge over many other types of service contracts. Instead of protecting a single product, such as your refrigerator or television, as other plans do, the coverage applies to a range of items, such as your appliances, home heating and ventilation system, plumbing and more, depending on the plan you buy. So if your air conditioner doesn't break, your washing machine or furnace might. That means there may be a better chance you...