The difference between the parts are that log and liniar scale the signal voltge differently. A log pot is better than a liniar pot for audio aplications. Log pots are more dificult to make than liniar pots, this may be a contributing factor to why the pots in your first 2 links are so different in price. The price difference may also be a factor of the company that makes the part. A more expensive part implies a higher quality part.
After looking at the data sheet, the one shown in the Farnell link (the one made by Vishay) has a longer mechanical and electrical life than the one shown in the RS link. It's mechanical life is 25,000 cycles minimum vs. 15,000 cycles for the linear pot. IMO you are getting more for your money with the log pot.