Besides IAS being a position under the Central Government and the HCS being under the State Government there are other differences listed below: 

While recruited as an IAS officer one works both under the State Government as SDM, DM and Secretary under the state government, as well as, under the Central government as Assistant Secretary, Joint Secretary, Additional Secretary and Secretary to the Government of India. While as an officer of HCS, you can only serve the state of Haryana.
While joining the IAS Officer will be an SDM, while an officer under state Civil Services would be lower designation as BDO.
Opportunities for promotion are more in the case of IAS officer than people serving under the state services.
Respect of an IAS officer is much higher than that of an officer of state civil services.