I think the 'rules' aren't clear, and that's the cause of the problem.
If you want to argue that all Steam Early Access (SEA) games should always be cheaper than at release, I would agree that this is in the best interests of the consumer (at least short term). However this in itself is not a justification for why it should be cheaper, just what benefits the consumer more. I don't think it's necessarily fair either, as surely SEA has some value to its customers beyond the base game, else why buy it? And SEA purchasers are under no obligation to provide feedback to the developers either, though it is not unreasonable to feel deserving of some recompense in the form of a discount on the game if they do. So what are the expectations of SEA customers?
It seems the real issue here is transparency of the cost structure for the game during development to release.
I would argue that developers should be able to set any price point they wish (according to what they feel their game is worth and what the market will allow them to get), but must make clear if (and how) the price will vary over the course of the early access period and what the final cost of the game will be at release. Further, customers should be made aware that the game may go on sale prior to release. So consumers would then have the information available to make an informed decision regarding their purchase and set their expectations accordingly.
