Hi Mr Captainsir, two factors are relevent as far as i know.
Firstly hubpages does count your own views in the total number of views although they are seperated out (don't count) towards hpad earnings (if you're set up for that).
The other factor is that in relation to adsense hubpages operates a revenue sharing setup with all hubpages members.I believe this works on a 60/40 basis in favor of members.This means that 60% of the time that your hub is being viewed will it show up in your adsense a/c and only clicks that occur during these times will earn your a/c the credit.The other 40% of the time any views and clicks will be credited to hubpages.
What counts as a view (in terms of duration etc) may also be slightly different between hubpages and adsense but i'm not 100% sure on that.
Baring these factors into account your 71 adsense views is probably a representation of 60% of your 250 views after you have deducted the number of your own page views and possibly also indicative of the difference between what hubpages and adsense record as a view.Hope that makes sense :-)