Transaction fees for smaller transactions
The default fee is in place to decrease the chance the creation of dust outputs (miniscule amounts of bitcoin). Dust outputs cost more to spend than they are worth themselves and they still need to be stored in the disk space of anyone that stores the complete blockchain - thus are frowned upon.

To read a discussion on that matter with some of the Core Developers you might want to review The minimum transfer fee is not trivial anymore.

Currently, there are some mining pools that accept transactions even without transaction fees. The default transaction fee in bitcoin-qt has been lowered before when the value of bitcoin increased sufficiently to make the recommended transaction fee too high. This happened for example in May 2013, when the default fee was reduced to 0.0001 BTC from 0.0005 BTC.

It is therefore expected that the default transaction fee will be kept at a respectively low level should the value of bitcoin increase dramatically. In any case, anyone can choose to ignore it by changing the settings of their bitcoin-qt.