There are the same. But rotary hammer have 1 more function which is just a hammer. Rotary hammer drill have drill only, hammer drill and hammer. Rotary hammer provide more punch joule compare hammer drill.

I wish to get the rotary hammer if I knew it exist at that time. Make my DIY work much more faster.

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Added on August 29, 2012, 12:52 am
No need so hardcore lah. We are small time DIY only. Rotary hammer drill will do the job.

You can use hammer drill to hack too. Hammer drill the hole along the line that you want to hack. As many as possible. Than slant your tools and hack drill connect the hole along. Finish up with some chisel and hammer. It is a bit slow. But still can do the job.

I think it'll take a longer time using a hammer drill. Maybe acceptable for DIY, but not so good for a professional. I think a rotary hammer drill would be a good choice, but of course it depends on the kind of DIY work you'll be doing. Different products for different needs
I think we'll agree to disagree here. Both are similar, yet different tools. They perform similar functions, but operate in a slightly different manner, so they cannot be the same tool. A hammer drill is not powered by a piston AFAIK.