[brofallon]

Just to clarify, exons are the portions of genes that code for protein sequence (they are expressed). Introns span the distance between exons and may contain regulatory or splicing information. Areas between genes are referred to as intergenic, and also may contain regulatory sequences that affect how genes are expressed.

Part of the issue with centromeric or telomeric sequence is that not only is it hard to sequence (being super repetitive), little is known about what a sequence variant in such an area might mean. It's kind of a chicken-and-egg issue: it doesn't get much attention because no one knows how to interpret variants there, and since no one knows how to interpret variants there it doesn't get much attention