You really need to throw "quickbooks" and sage (and other related search terms) in there to get the true picture. Quickbooks still way more popular as a search term.
https://www.google.co.nz/trends/expl...z=Etc%2FGMT-13
Also, compare Xero to Quickbooks online in the US - https://www.google.co.nz/trends/expl...02rsj7z&geo=US
The picture looks better if you compare the two worldwide:
https://www.google.co.nz/trends/expl...ne,+/m/02rsj7z