RSA/DSA: Wouldn't it make sense to sign using decoding the data hash? Why is encoding using the private key used for signing? Wouldn't it make sense to keep the premise, that private is for decoding and public is for encoding? i.e. create a hash and threat it as a result of the crypting and decrypt it. The decrypted value being the "signature". Than when someone want to validate the signature, he would encrypt the signature and he would get the hash. 

Am I missing something? Why is this not used?
Your question appears to be "why do we use the terminology 'encoding' when talking about what we do as a part of the signature operation".  Well, we don't (at least, I don't, and I don't remember hearing that terminology from someone else).

As for RSA, well, the terminology you use is moderately irrelevant (as long as you do the cryptographical operations correctly, it doesn't matter what you call them); on the other hand, encoding would appear to imply that you are taking a 'signal', and putting it into a different representation, while decoding would appear to imply that your reversing that operation, and are putting the signal back into its original state.  While I suppose you could call the signature operation an "encoding" one, calling it a "decoding" one would appear to me to be an abuse of the terminology.

AS for DSA, well, your description of "encrypt the signature and he would get the hash" is not how DSA verify works; instead, the verifier inserts the signature, values from the public key and the hash into a formula, and if both sides of the formula are the same value, then the signature verifies.  There's nothing that can be usefully described as "decoding" here.