Quoting now from Stephen J. Gould (1992):
> I do not say that these criteria are free from exceptions; nature is nothing if not a domain of exceptions, where an example against any clean generality can always be found. Some distinct populations of plants, for example, can and frequently do interbreed with others that ought to be separate species by all other standards. (This is why the classification of certain groups--the rhododendrons, for example--is such a mess.) But the criteria work in the vast majority of cases, including humans.
Since then we've learned a lot more about bacteria, which employ horizontal gene transfer. This completely breaks the traditional model.
Our own human cells can also pull off some odd tricks. See http://en.wikipedia.org/wiki/HeLa#New_species_proposal for one proposal for why HeLa cells should be considered its own species. (Note also the mention of special rules for an independent unicellular asexually reproducing species.)
I noticed that your understanding of 'species' doesn't consider obligate parthenogenesis. There are, for example, some 50 species of lizard that only reproduce parthenogenetically. Under your definition, these are not a species because there is no mating. I submit that that is a much more critical shortcoming than a ring species.
Perhaps your objection is more based on a lack of knowledge than anything else?