I've thought a bit about this too and agree that $4 is absolutely the correct cost for it. However, Donald has said there will never be such a card, not necessarily because it would be boring (which it would) but because it would limit how variants of the card could be priced. See "The Vanilla Card Problem" section of this:
http://forum.dominionstrategy.com/index.php?topic=121.0The solution to the vanilla card problem is not to do vanilla cards. If your basic version of a concept includes a bonus, you can vary the bonus and keep the cost the same. Only when you do the bonus-less version are you stuck with increasing the cost. But you can't just not do vanilla cards. You need them for how simple they are. So in the end you pick and choose. For example Dominion does not have a card that just says "+1 Card +1 Action +$1." If I made that card, it would limit what other cards I could make. So instead I just do variations on it.
With the present set of official cards, I don't see a problem with having that card at $4, but we don't know what other official cards are yet to come. And even if none of those pose a pricing problem for the vanilla version, I can still see how it was smart not to limit future development by creating it.
But yeah, for me the real reason is just that it's boring. A $4 Peddler would be a no brainer. There would be no reason not to buy the card, since it can't harm your deck and provides you with money. The actual Peddler is interesting because of the cost games you can play. Market and Bazaar (the latter of which you missed in your list) are interesting because you usually need to be able to make use of their extra abilities to justify blowing $5 on them. Oasis is interesting because you need a certain type of deck to reliably get the benefit out of it. And so on.
A $4 vanilla version would not only lack these interesting gameplay dynamics but
actually detract from the gameplay dynamics of all these different variants, since its presence on the table would provide a complication-less way to reap the same main benefit.
Edit: Grand Market and Conspirator probably belong in your list, too.