CapnZapp
Legend
The problem is discussed elsewhere. Here is the thread for solutions! 
Suggestions...
1) Ban potions outright
2) Make them exotic (players can't buy or create them)
3) Increase their price
Myself I'm inclined to view the idea that a high level potion should grant a higher resistance as fundamentally flawed.
Resistance 5 might not stop as much of the incoming damage at Epic level as it does at Heroic. But at Epic level you have a truckload of hit points and several mind-boggling tricks up your sleeve.
I am postulating that resistance 5 is about as (very) valuable at Epic level as it is at Heroic level. This makes the Adventurer's Vault potions egregious errors in my book.
4) Instead, a Potion of Resistance should always grant resistance 5. The (much) higher price at Epic level should instead be motivated by it granting Epic Resistance, while the heroic potion only granting Heroic Resistance.
In other words, the level 4 potion grants resistance 5 that is effective only against monsters of levels 1-10. The level 14 potion grants resistance 5 that is effective only against monsters of levels 1-20. And the level 24 potion grants resistance 5 that is effective against all monsters (or possibly only the ones below level 31, if you feel nasty as a DM).

Suggestions...
1) Ban potions outright
2) Make them exotic (players can't buy or create them)
3) Increase their price
Myself I'm inclined to view the idea that a high level potion should grant a higher resistance as fundamentally flawed.
Resistance 5 might not stop as much of the incoming damage at Epic level as it does at Heroic. But at Epic level you have a truckload of hit points and several mind-boggling tricks up your sleeve.
I am postulating that resistance 5 is about as (very) valuable at Epic level as it is at Heroic level. This makes the Adventurer's Vault potions egregious errors in my book.
4) Instead, a Potion of Resistance should always grant resistance 5. The (much) higher price at Epic level should instead be motivated by it granting Epic Resistance, while the heroic potion only granting Heroic Resistance.
In other words, the level 4 potion grants resistance 5 that is effective only against monsters of levels 1-10. The level 14 potion grants resistance 5 that is effective only against monsters of levels 1-20. And the level 24 potion grants resistance 5 that is effective against all monsters (or possibly only the ones below level 31, if you feel nasty as a DM).