The more common related concept here is "highly conserved", meaning a sequence that is difficult for an organism to change and still remain viable.
Every base pair of DNA is potentially subject to change via copying errors and other sources of genetic perturbation. Many such changes, however, will break something important and not produce a viable organism. This is true both for big, complex organisms like people and also for small, simple organisms like bacteria.
The more fundamental a region of DNA is to the operation of a cell, the more difficult it will be to change without breaking, and thus the more highly conserved the sequence is likely to be. That generally means that the conserved regions are either protein coding sequence or functional RNA sequence. Likewise, the most highly conserved are the ones involved with core cellular activities such as transcription, translation, and replication (see citations below) --- which are exactly the type of sequences identified in the reference that you link.
Now, since 2007 we've dramatically increased the number and diversity of organisms whose genomes have been sequenced, and it's not clear to me whether their purely invariant sequences will have held up. Those areas are certainly quite highly conserved however, and that is only to be expected.
Bottom line: the probability that a DNA region is conserved is highly dependent on it being a coding sequence or functional RNA.
Some relevant citations on the nature of highly conserved sequences:
- Isenbarger, Thomas A.; Carr, Christopher E.; Johnson, Sarah Stewart; Finney, Michael; Church, George M.; Gilbert, Walter; Zuber, Maria T.; Ruvkun, Gary (14 October 2008). "The Most Conserved Genome Segments for Life Detection on Earth and Other Planets". Origins of Life and Evolution of Biospheres. 38 (6): 517–533. doi:10.1007/s11084-008-9148-z
- Harris, J. K.; Kelley, S. T.; Spiegelman, G. B.; Pace, N. R. (12 February 2003). "The Genetic Core of the Universal Ancestor". Genome Research. 13 (3): 407–412. doi:10.1101/gr.652803.
