It's pretty simple really.....as in the link above.
If your offering lets say carpet wet cleaning (HWE) on one web site and also dry cleaning of carpets on another, Google will not let you serve 2 adds because you would then be able to direct 2 adwords adds to your business.....although they would be two different web sites.
Therefore, you could have 2 adds for lets say ''carpet cleaning London'' either dry or wet, that would take up the two top positions.
Whereas in effect you could offer the same options on one web site.
The alternative is to have 2 google accounts and 2 bank accounts.......but I suspect you would be found out and risk having your accounts brought to an end. If Google didn't notice it, one of your competitors probably would.