The measure, which the House of Representatives passed in May 2005, allows couples who have had embryos frozen for fertility treatments to donate them to researchers rather than let them be destroyed.
....
In August 2001, Bush announced that his administration would allow federal funding only for research on about 60 stem-cell lines that existed at the time. Researchers have since found that many of those lines are contaminated and unusable for research.

CNN.com - Bush vetoes embryonic stem-cell bill - Sep 4, 2006


Also, let's be perfectly clear on what the phrase "stem cell lines" means in the first place.

5. What is a stem cell line?
A stem cell line is composed of a population of cells that can replicate themselves for long periods of time in vitro, meaning out of the body. These cell lines are grown in incubators with specialized growth factor-containing media, at a temperature and oxygen/carbon dioxide mixture resembling that found in the mammalian body.

Embryonic stem cell lines, both human and mouse, can be grown indefinitely in vitro if the correct conditions are met. Importantly, these cells continue to retain their ability to form different, specialized cell types once they are removed from the special conditions that keep them in an undifferentiated, or unspecialized, state.

A limited number of human embryonic stem cell lines have been approved for use by scientists receiving federal funds in the United States. In August 2001, President Bush mandated that if scientists were using federal funds, research could only be conducted on the cell lines that were already in existence, grown from fertilized eggs that were to be discarded at in vitro fertilization clinics.

This regulation stated that no additional human stem cell lines could be generated from additional blastocysts. In the long term, this will place severe restrictions on the scientific process in this field and will limit the ability of scientists to compare the potential of human embryonic stem cell lines for tissue repair, to that which can be accomplished from other sources, such as adult stem cells.

ISSCR :: Stem Cell Science : Frequently Asked Questions

We are talking about "stem cell lines" / stem cell samples that originate from the source DBear talked about.

Bush is effectively saying "Well, you've got X amount of toys that you have been playing with, and we're only going to fund you for that X amount of toys. If they break (contaminated), then that's tough..."