At least 80% of the population of all western countries earn negative net income from profits, rents and interest (income from capital) and still depend for 100% of their 'financial value' on their labour. Interest earning pension funds, savings accounts and so on do not change this fundamental fact and are largely irrelevant to the class structure of society. Besides, building societies and credit unions were among the first innovations of the proletariat. There has never been a proletarian class which did not have interest earning savings accounts.
On the other side of the coin, the owners of capital have often chosen to work to maximise their profits. Your distinction is sophistic and purposely obfuscating - similar in its aims to the same point when made by Tony Blair.
I have never subscribed to the Maoist theory of labour aristocracies and the proletariat of the third world is similarly complex to the proletariat of the first world, with savings accounts, interest raising loans and so on (even on the tiny scales that they deal in). Your apparent belief that as soon as somebody earns a cent in interest, they are no longer a proletariat, would probably rule out over 90% of the world's working class, present and historical.
The sort of nit-picking definition that you are using to define classes here makes no sense. In the domain of the social sciences, trends, relations, forces and generalisations are the limit of our ambitions. There never was a homogeneous, well-defined working class and bourgeois. The concepts describe general classes based on the dominant relations to capital and labour that the members of the classes have.
