AZN.... excellent chart!

I'm not disagreeing with your conclusion, but your premise is a bit shaky.
20% of revenues - yes, but globally.
$4.6bn in actual fact, of which Europe accounts for $1.1bn.
Additionally, AZN has "process, method-of-use and additional substance patents with expiry dates ranging from 2009 through to 2019. In addition, Nexium has data exclusivity valid to 2010 in major European markets."
Furthermore, any generic copycat pill would have to meet stringent regulatory tests before being released. AstraZeneca holds exclusivity over data published on Nexium's efficacy and safety until 2010. Only after that (apparently) will generic drug makers be able to use that data to support clone products. Whether they need to use that data I do not know.
The issue that is likely to drag on shares is that AZN is also facing patent challenges over those other patents in the EU, and over the main substance patent itself in the US perhaps as early as next year. A clone can apparently be launched in the US even before a successful challenge to the patent.
The pipeline is apparently crap. The only slightly bullish points I can see on the horizon are that the P/E is approaching single digits, and the yield must soon be approaching 5%, but this is all at first glance.
There must be an army of longs wanting to get out at 28 quid, which I guess is reason enough for the price not to get even close.
So in short, crap prospects, but cheap, but yes, liable to get cheaper. If only I could bring myself to sell....