why would acetic acid concentration of a good vinegar need to be known for commercial reasons and regulatory health and safety reasons

Answer 1

'Vinegar' covers a great many products that are made from a many substrates.

Table vinegar is about 5% whereas pickling vinegar is significantly stronger 15-20%. You might want to check these figures as they are from memory. Thus from a commercial point of view, i.e. what the product will be used for, the concentration is important.

The H&S side will depend on the country that you are in, as different countries have different regulations. The main ones to look at
1.are those concerning medicines (as vinegar is used as a medicine)
2.those concering the control of hazardous substances (=COSHH in the UK)
3.those concering food products
4.those concerning transport of bulk materials as it is shipped by tanker.

Of interst to you might be the Safety data sheets see:
http://msds.chem.ox.ac.uk/AC/acetic_acid.html

However, vinegar is a dilute aqueous solution of acetic acid. If you drink enough vinegar, you (unsurprisingly) won't feel too well. However, the data sheet for acetic acid (link above), which outlines the hazards presented by the pure acid, should not be taken as representing the hazards (which will be different) which might be associated with vinegar.