Imo it is the only way for this tank not to leak value and thus be a worthy place to store value at all.
As long as people in 2013 still need their anonymous purchases, Silk Road merchandise or non-reversable escrows etc, bitcoins will have significant value (doesn't have to be gigantic sums, but definitely a bit more than it costs to mine them).
I don't see any logically compelling reason why demand would decrease over the years.
Bitcoin fills a very specific niche that has had demand since the advent of the internet but was never materialized until 2009.
As the reward first halves to 25BTC per block and then to 12.5, it will be a seller's market.
There will be much, much less fresh BTC going around but also much more people wanting to get ahold of some just to conduct certain types of online business.
Also, as the blockchain grows longer, the less incentive competing cryptopcurrencies have to start their own.
People will obviously be drawn to the network most resilient against attack.
