My understanding is that real money (let's say USD) have value because, thanks to loans/mortgages that are done in USD, you have a garantee that some people will always be really motivated to get some USD, to pay their loan/mortgage. Since those tends to last 20-30 years, that's good because in 20-30 years you know that your USD will have value to someone (to many people even)
On the other hand, no one really need to get bitcoins. It would not be surprising than in 20-30 years, no one cares about it (and it is actually the most likely scenario IMO).