Actually you are incorrect Jeff, Lydia is given in Whiterun, and she comes to you automaticallly even w/o buying the house. The housecarl in Riften is Iona and you only get the housecarl once you become thane in that town. Whiterun is the only town you become thane in prior to buying property. So in Riften if you bought honeyside but didn't complete the missions to become thane then that is why you don't have a housecarl