I fear this question can not really satisfactorily be answered by science.
> Could it be that intense speciation and specilization is a
>natural result of the quick and forced evolution we discussed, caused by
>the changing climate in Australia over the past few million years? Why
>should the species become specialists and not remain generalists?
This one is somewhat easier. Rapid species diversification
("specialization") is a phenomenon associated with adaptive radiation. And
the latter process can be assumed to have occurred (not only in _Dosera_)
when the climate in W and later SW AU changed from temperate to
mediterranean type (creating new biotopes).
>Or is it better to have a large number of
>specialists to survive constant habitat changes?
Yes.
> Is it possible for numerous generalist species to live together in a small
>area and compete for similar necessities?
Possible but more difficult (frequently leading to extinction of one or
several of these taxa).
> I wonder if the numerous Nepenthes species found in Borneo, for
>example, are each specialized in trapping specific prey, being
>pollinated by specific insects (which would be a natural barrier for
>mass hybridization), and growing in specific habitats (altidudes
>included)?
Only the last seems likely (prey - mostly ants - and pollinators - mostly
flying insects - seem to be rather unspecific).
Kind regards
Jan