There is no reason for MSI to clamp reflection samples seen through glass with completely sharp refraction, as it would probably not create fireflies. Keymaster himself told me he thinks that particular situation could be improved, while still keeping MSI low.
Also, what you say is exactly what is happening. Only very few people bother with something unbiased like Maxwell, because the accuracy difference it makes is nowhere near worth the never ending rendertimes. That's why Vray has became mainstream. And there are many and many examples such as Bertrand Benoit or Peter Guthrie that renderer does not need to be unbiased in order to achieve realistic results.
People who are not skilled enough will never be able to achieve great results even if the use Maxwell, on the other side, those who know what they are doing will not have any problem achieving great and photorealistic results even with Vray or MentalRay.