It is indeed. The licence fee pays for RTE's public service obligations - news, current affairs, sport, childrens, history, etc.
Advertising, sponsorship, programme sales and other commercial activity generate the rest from where the all the so-called 'stars' earn their money.
AFAIK, during the boom years, RTE earned more from the latter than it did from the licence fee.
Big names like Kenny, Tubridy, Joe Duffy, etc, earn serious money for RTE through advertising - that's why they command the salaries they do.
If Tubridy was to up and leave there would be panic in Montrose because his shows generate so much dosh for the station.
It remains to be seen how the death of Gerry Ryan will effect RTE's revenue - his radio show alone pulled in between €5m and €6m a year in advertising. He was paid around a 10th of that.