One major difference between adult and embryonic stem cells is their different abilities in the number and type of differentiated cell types they can become.
Scientists believe that tissues derived from embryonic and adult stem cells may differ in the likelihood of being rejected after transplantation.
They have actually managed to make adult stem cells pluripotent (research at the UW Madison did this), and furthermore have managed to make them from a person's own skin (again, UW Madison ftw). And adult stem cells are less likely to be rejected. Embryonic stem cells grow at a different rate than adult stem cells (they grow much faster) which causes higher rejection rate and can in fact act much like a tumor.
The difficulty isn't being able to research them. There's a lot of money flowing both ways that is very politically motivated, but it's pretty simple to say that the adult stem cells have actually resulted in recoveries and cures (embryonic have not) and do not have the ethical problems. Being able to research embryonic stem cells doesn't make them more viable. At this point, they don't have advantages.
http://stemcells.nih.gov/info/basics/basics5.asp
One major difference between adult and embryonic stem cells is their different abilities in the number and type of differentiated cell types they can become.
Scientists believe that tissues derived from embryonic and adult stem cells may differ in the likelihood of being rejected after transplantation.