The number of bitcoins has a limit,this constrains the market availability and the behavior of the value. Bitcoins are divisible in infinite number of parts, so this facilitates the situation on the market space.
There is a mathematical explanation for having around 21 million limit:
Calculate the number of blocks per 4 year cycle:
6 blocks per hour * 24 hours per day * 365 days per year * 4 years per cycle = 210,240 ~= 210,000
Then you can sum all the block reward sizes (rewards are divided by 2 every 4 years):
50 + 25 + 12.5 + 6.25 + 3.125 + ... = 100
Finally, you multiply the two figures:
210,000 * 100 = 21 million.
The estimation is to reach this limit around 2033.
The question is that the reward to complete a block is decreasing with time. Could it be the case that one day to mine bitcoins is not profitable?
The legal aspects of use in terms of virtual currencies are evolving differently. In Canada and US there are currently specific laws and taxation fees for these environments. Other countries are lagging from these areas. The EU is still not communicating a common pathforward about virtual currencies.
There is a lot of evolution on legal aspects and the number of transactions to be done
There are a good bunch of companies that are communicating that they will enable transactions with bitcoins by 2019.