I use both G10 & SLR for photo. Normally I use wide angle or short distance object with G10 if I do not have time to change the wide angle lens to capture the object because I put zoom lens (70-200) in my SLR.

You can use G10 in manual mode similar with SLR. There is an optional teleconverter for G10, but I am not recommending you to use teleconverter as the result was not good.

Just consider the purpose of the camera. if you like simple and like taking landscape or short distance object - G10 is good option. But if you plan to buy additional lens, buy SLR.