Sure, but the spec is upon what they can actually hang their hats. Personally, under the right kind of driving conditions, as determined by the OLM, 10000 miles is attainable on a good conventional that meets the specification. Note that a lot of the 5w-20 options are blends anyhow, and anyone using a 0w-20 is using a blend or a synthetic.
Of course, you bring up the issue, indirectly, of trust, and that's valid. One is perfectly free not to trust the OLM for 10000 miles on a conventional, even with the correct specification, and it could be that such an interval is out of reach. There certainly is precedent for that. But, then the specification or the OLM intervals are at fault, not us, really.