Did you think about that what will happen in e.g. 2050 with this 'bitcoin chain'? Will it increase from 8GB to e.g. 8TB? 
If bitcoin ever goes mainstream I think 8 TB is too low to be considered a reasonable estimate for the year 2050...
Actually I think it's too high given the current protocol.
Assuming the protocol doesn't change, there is currently a 1 megabyte maximum size for a block. A block is added to the blockchain approximately every 10 minutes.
So, there is a maximum (on average) of:
6 megabytes added to the blockchain every hour.
6 MB * 24 hr = 144 megabytes added to the blockchain every day.
144 MB * 365 days = 52,560 MB / 1024 MB per GB = 51.33 gigabytes added to the blockchain every year.
51.33 GB * 37 years = 1900 GB / 1024 GB per TB = 1.85 terabytes added to the blockchain by 2050.
51.33 GB is approximately 0.05013 TB, so to reach 8 terabytes in size, it would take:
8 TB / 0.05013 TB per year = 159.6 years (which is more like 2172 than 2050).