Some doctors will do more than necessary, if they either have a fee-per-service insurance-related issue (as Medicare has worked), or if they are concerned about potential malpractice accusations, and want to cover their butts.
You don't hear much about doctors doing less than necessary, though this could happen after 2014 when the health reform act is more fully implemented. There are provisions that are set up to essentially allow doctors to be paid for treating patients "appropriately," rather than excessively (doctors could be more prone to missing things). It sounds to me like the doctor genuinely didn't think you needed an x-ray or whatever, though you could have requested one.