Solidity Opcode Documentation – Where to Find Opcodes 0xFE and 0xFD

Even though I do not know the real reason, I will try to guess. There would be the following considerations:

1. Size of the namespace. There are not so many possible opcodes, so these need to be allocated very sparingly. The space of contract addresses, on the other hand, is practically unlimited for all practical purposes.

2. Risk of name re-use. It is a good software engineering principle not to reuse names (or opcodes), especially in the system where one does not control the upgrades.

3. Utility. There are some operations that are always useful, like arithmetic operations, bit twiddling, flow control and others. Cryptographic primitives, on the other hand, may be in the future proven inadequate, and something else will be used instead. Making such primitives into opcodes is taking a risk of spending valuable namespace on something that could become obsolete.

4. Gentle promotion of popular/useful code. If certain things, for instance, zkSNARKs operations, or Dogecoin PoW verification, starting with solidity code, then being partially optimised, become very useful and popular, they might become pre-compiled contract. Such promotion is a much gentler change to the network than introducing a new opcode.

I'll leave the precise interpretation of the OpCodes to someone else and just point out that they are different instructions so different implementations are to be expected.

According to this: http://solidity.readthedocs.io/en/develop/control-structures.html#error-handling-assert-require-revert-and-exceptions

Starting with Metropolis, revert; will return unused gas whereas throw will continue to consume all available gas. In terms of contract state changes, they are the same - everything gets rolled back.

Hope it helps.