I just replaced the HDD in my laptop with...
Why? I use the thing for web browsing, messing around with photos, watching iplayer and composing documents..... and a 1TB HDD was £46 including next day delivery.
Yes, an SSD would be faster, but I already had about 220GB of stuff on my old hard disk, so it's not hard to see that a £70-£80 240GB SSD wouldn't be up to the job for long, so I'd have to fork out even more for a ~500GB SSD.
I have difficulty believing that the price per GB of a given SSD size actually reflects the relationship between development/manufacturing cost and capacity.