First, most recruiters/hiring managers ask for current comp (or at least a salary range) early in the discussion, so it should be easy for them to offer well over someone's current pay. This simply removes one bargaining tools (lying about current comp) for an employee considering a move elsewhere.
Second, matching outside offers very quickly becomes a slippery slope. Anyone who figures out that such a policy exists will quickly come to the realization that the easiest way to get a raise is to put themselves onto the market. That's toxic, not to mention unsustainable.
Finally, equity. The one-year cliff exists for a reason, and if you're playing for keeps with an early-stage startup, you're probably expecting (or at least hoping) for your ownership stake to be worth a lot more in the long run than your salary.