Taken trait-by-trait, when the parents of a hybrid differ in phenotype, the phenotype of the hybrid is more likely to match one of the parents or the other than a blending of the two. That is to be expected in Mendelian heredity. Traits that blend (such as blood types A and B) are far less common than those that show a dominance-recessive pattern.
If the hybrid then breeds with a member of either original 'purebred' population, the next generation will have a genetic composition that is weighted approximately 3:1 in favor of one of the parent populations, both in DNA genotypes and in phenotypes.

Interesting that they possess different numbers of chromosomes but are able to interbreed, AND their offspring are not sterile.

"the findings are not universally accepted". So effectively so, they should be labeled "universally" I believe. Article self-inflation of importance, more likely.

@ Donutz: Not uncommon, it happens a lot among horse species and happened in apes (humans vs the rest). Apparently this monkey clade is a howler, with each and every one having their own and often multiple chromosome number, especially for sex chromosomes.

Examples of species with multiple numbers in the same population [species names excluded, the table didn't C&P easy]:
2n=48-51 (Minezawa et al., 1985)
2n=47, 48, 49 (Lima & Seuanez, 1991)
2n=47, 48, 49 (cited by Lima & Seuanez, 1991)
Multiple sex chromosomes (Rahn et al., 1996)
2n=49-52 (At CRES)
2n=48 (46) (At CRES)
[ http://placentati...ler.html ]

In another paper it seems to be that the resulting morphological differentiation is often connected to the voice box, so it helps sexual selection and speciation in these species.

Taken trait-by-trait, when the parents of a hybrid differ in phenotype, the phenotype of the hybrid is more likely to match one of the parents or the other than a blending of the two

I can think of one example where this doesn't happen. Ligers, for example, share traits of both African Lions and Tigers. And you end up with an animal with a unique blend of traits.

There are many other such examples where the resulting offspring is a combination of traits from parent species.
http://en.wikiped...ology%29

Interestingly sex is the most important characteristic when crossing lions and tigers.
Female lions are much better at suppressing the competitive male growth signals, because they live in prides. Growth dysplasia in cats.

Male lion x female tiger = liger (HUGE, 800lbs)

Male tiger x female lion = tiglon (meh, 400lbs)

Phenotypic expression rarely exists in mendelian ratios of vertebrates because of the large number of trans-acting regulators.