I used to work at a large, well known AV company. While much of what other commenters have said is true, I will note that VT is less authoritative than some realize; the version of our product that VirusTotal was given access to was substantively different than our normal product; features such as sandboxing were removed.
I wouldn't be surprised if this was a common practice; we considered our product's detection capabilities to be proprietary.
I wouldn't be surprised if this was a common practice; we considered our product's detection capabilities to be proprietary.