I guess there is a difference in the fact that gift certificates are always devaluing with monetary inflation, whereas prepaid credit can be used to purchase a service which is just as energy intensive (cost to provider) in 10 years, as it is if used in the next month. Yet in 10 years, the cost to the provider will be more to deliver the same energy (due again to monetary inflation).

There doesn't seem to be a neutral option here, because it's very hard to account for inflation without the holding party paying dividends at the exact rate to offset it.