With residential stairs, no riser should be higher than 8 inches. This requirement is so commonly violated at exterior residential stairs that some inspectors may tend to let it slide. By so doing, they subject themselves to a measure of liability, as demonstrated by your current concern. However, in such cases, there is another consideration. In the course of a home sale, irregular stair risers and settled walkways are not the types of defects that a seller would be likely to repair.
Most sellers are willing to pay for the repair of such items.
With a settled entryway, however, it would be unusual for a seller to fix the problem. Such problems, when they appear in a home inspection report, are regarded as disclosure information for future consideration by the buyer. Your home inspector was probably remiss in failing to disclose this condition, but in all likelihood that failure did not alter your decision to buy the property or your demands upon the seller. I'm negotiating the purchase of an older home and would like the seller to provide a termite inspection. The seller refuses to have this done, and I'm worried about buying a house that might have termite problems.