It kinda does set a price floor, the cost of operation of the cheapest miner is the price floor. No miner will want to sell below as it would be a loss and considering Bitcoin is deflationary in nature, it is likely worthwhile to just hold the coins and earn the deflationary interest on them until the price adjusts.

Assuming you can only either sell or loose the money fails to take temporal effects into account, ie the fact that there is such a thing as time progressing that changes variables.