Aricept is Donepezil Hydrochloride (empirical formula of C24H29NO3HCl,
http://www.rxlist.com/aricept-drug.htm).
Aricept is the trade name is was branded under when it was first licenced after the licence runs out (usually 15 years) then it can be made under a generic name.
Aricept when it came out was very expensive and so rarely prescribed so when the licence ran out 2 years ago we all celebrated on here and now just about everyone gets it
http://www.alzheimers.org.uk/site/scripts/press_article.php?pressReleaseID=769
Any perception that the branded product is better than the generic one it probably just that a perception other than some colouring it's the same thing.
It's a shame the system works this way many medicines are so expensive NICE won't licence them on grounds of cost, cancer drugs are an example and specifically some breast cancer drugs, it's no use to you if you have cancer knowing that in a few years time when the drug goes generic you'll get it, you need it now.
My wife got on Aricept "as a trial" before it was generally available, since then she was moved on to Donepezil, I've never noticed any difference.
I think it's just a case of Waitrose beans taste better than Aldi ones because they cost more, if your doctor said they would/are only allowed to prescribe Donepezil I wouldn't be surprised, why waste NHS money.
K