How singulars vs plurals are handled varies by both the SE and the Advertising platform.
For example, see
concert ticket - Google Search
and
concert tickets - Google Search .
Note that:
1) The organic listings differ, with the singular returning approx. 1,880,000 results, while the plural yields approx. 20,400,000, a substantially greater number.
2) The paid listings also differ. Looking at that listing which appears in the 1st position for both, each from the same advertiser, we see that each is specifically targeted, one to "ticket" and the other to "tickets."
http://www.google.com/aclk?sa=l&ai=B0KWwq1FgSLPuNJ7eeJmOjeIG1fK0VKeFuooH 2saOB5DWJwgAEAEYASCnxp0GKAI4AFCQ65vc-P____8BYMn2pozQpOQPoAHDs_79A8gBAdkDLpAFOPtD_lM&sig =AGiWqtwmNBazF3Eu2vHkF0g7wDkB4IjUkQ&q=http://www.ticketsnow.com/Concert_Tickets.html%3FGCID%3DS16598x002-genr_cncrt%26keyword%3Dconcert%2520ticket
http://www.google.com/aclk?sa=l&ai=BKypbxVFgSJOrC4beeYWliNkG1fK0VI-IuooH3OKSBoCfSQgAEAEYASCnxp0GKAM4AFDN5I0HYMn2pozQp OQPoAHDs_79A8gBAdkDLmb8tvOAAkM&sig=AGiWqtwVFcsCvnk gONeDvvHeru1IRSjohw&q=http://www.ticketsnow.com/Concert_Tickets.html%3FGCID%3DS16598x002-genr_cncrt%26keyword%3Dconcert%2520tickets
By targeting each separately one can independently position the bids vis-a-vis competitors' bid, so that no more is paid than is necessary.