our preference is always to find out why the block is happening and try to convince people it should be otherwise; widespread abuse of robots.txt does no-one any good, having been crawling and indexing for so long it’s a standard that we understand and are quite fond of
we can see some of the perils and pitfalls of it too, but web builders need to be given some tools and assurances that those tools will work for them
probably a sample size issue, we crawl and index everything we are able to; have seen many of this kind of site in the past, and finding them is something that other people have said they enjoy about mojeek