Not in the US, although implementation patents are easier to defend you can write very broad patents.

You can have a business method patent, eg look at the prices charged by various retailers and buy the lowest one, or even a patent on the plot of a novel. Both of these have been patented in the US.

Your 'invention' no longer has to be workable for it to be patented nor do you have to demonstrate a working implementation.

That's the issue with a lot of software patents on things like H264 - the patent can simply be on the concept of compressing video, you don't have to invent a particular encoding scheme.