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Print-style 'debugging' output provided by Bengt Richter in 
a follow-up in the c.l.p. thread "Issue with new-style 
classes and operators" showed that 'a+1' worked because 
of a __getattr__ call getting '__coerce__' (rather 
than '__add__') and that 'b+1' did not trigger such a call.  
So I presume the quoted parenthesized statement about 
__coerce__ and 'new-style numeric API' was meant to 
explain as least this part of the change in behavior.  
However, it is still not clear to me, even after reading the 
development (2.3a) version of the ref manual, why failure 
to find '__add__' in 'the usual places' (to quote RefMan 
3.3.2 __getattr__ entry) does not trigger a call to 
__getattr__, nor why the initial attempt to find it did not 
trigger __getattribute__.  The sentence 'For objects x and y, 
first x.__op__(y) is tried' (3.3.7) implies to me that there is 
an attempt to find __op__ as an attribute of x.  Unless I 
missed something I should have found, a bit more 
clarification might be usefully added.