Can't say I'm surprised regarding this, surprised they didn't do it sooner as its not exactly hard to clean up the image instead of paying them for it...
Too true - although you tend to lose quite a bit of fine resolution, and creating a map of a larger area at a decent scale is a helluvalot of cropping cutting, pasting and merging - not to mention correcting sheet boundaries and vintages to get a decent fit.
IMHO - they should be a free digital resource for research purposes (which covers most of us on AN - I don't think many of us actually hang them on our front room walls)
BTW: the National Library of Scotland has a pretty good map site too:
http://maps.nls.uk/ Quite a lot of non-Scottish maps as well.