hmm, hadn't thought of this but yes, in my Brit campaign currently I'm avoiding extermination because I desperately need population. But I am having a major problem with rebels -- they pop up about every other turn somewhere in my six provinces.

Good training for young Generals and diplomats, so it actually works out well. But I definitely did not see this much rebellion in my extermination-happy Scipii campaign, even though I had 42 provinces in the last turn I played.