No mystery there, gdog, the ones you mentioned are simply OEM's of the high quality alkalines
En's are literally damn near the bargain bucket of the alkaline world - hell, shop 'own brand' cheapie alkalines are often better performers.
Panasonic items are damn near as good as duracell, and when you can buy them in 30's for not a lot (look out for 'power tower' packs) - it's healthy saving if you dont wanna go down the rechargable route.
FG