Not so Indefinite

Melinda Penner at STR's blog points me to an article in Time on stem cell research which more balanced than most articles on stem cell research but left me scratching my head at an apparent inconsistency. (emphasis mine)

Adult-stem-cell research is morally fine but clinically limiting, since only embryonic cells possess the power to replicate indefinitely and grow into any of more than 200 types of tissue.

and then

Today there are only 21 viable lines, which limits genetic diversity. They are old, so they don't grow very well, and were cultured using methods that are outdated. What's more, the chromosomes undergo subtle changes over time, compromising the cells' ability to remain "normal."

On one hand we're told embryonic stem cell have this power to "replicate indefinitely" and then a couple of paragraphs later we're informed that old cell lines don't grow well and the cells change over time. If we're having troubling using stem cell lines which are less than 10 years old, should we really be claiming they can "replicate indefinitely"?

The article also mentions something which is often glossed over by embryonic stem cell proponents.

Extracting knowledge from embryos that would otherwise be wasted is one thing, but scientists admit that moving forward would require a much larger supply of fresh, healthy embryos than fertility clinics could ever provide.