If anything, it seems like an acknowledgement that the battery life is short and that the unit was designed to be charged on a daily basis if used regularly. The 3DS itself was designed as an "always on" device as well with features such as step tracking, Mii Plaza, Street Pass, Play Coins, etc. Nintendo clearly wants 3DS owners taking them whever they go.
The cradle doesn't offer anything other than "permanent" base in which to plug in your 3DS for recharging every day.
And while it's a pretty cheap attachment (hollow plastic shell, simple AC adapter plug to wire contact prongs for power), I see Nintendo dropping the cradle from future revisions in the interest of reducing packaging and materials. It literally doesn't do anything beyond taking up designated "3DS charging space."
If anyone, Nintendo included, wanted to add more battery power, a battery pack with a higher mAh rating would be better than any sort of clip on power device.
