First off, I do think BYU has some unique advantages, but I'm not really convinced that roster limits are the solution. Ultimately I think it comes down to some schools just are more attractive due to culture, academics, location, etc. and they have an easier time attracting top talent. BYU has this in spades, specifically:
1) There are a lot of really good mormon runners. Utah's HS running scene in particular has been nothing less than exceptional given its population the last few years.
2) BYU is ridiculously cheap in comparison to other schools at a similar level (tuition about $5k per year if you are mormon).
3) There is a lot of social/family pressure on mormons to go to a "church" school. I'm mormon from Utah and when I was looking at schools my parents pushed me very hard towards BYU, mainly as a means to ensure I married a good mormon girl. So despite the fact that Ed Eyestone had no interest in me whatsoever and I most likely never would have cracked into their top ten, the only reason I didn't go there was another coach took a chance on me and gave me a better scholarship than I deserved.
At the end of the day, even with a smaller roster, I think BYU's men's team would probably be just as good. I don't think it is accurate or fair to say that they burn through bodies. Ed Eyestone isn't an idiot and he clearly recognizes he can train his team hard and based on what my friends on the team have told me, there is a lot of internal competition for traveling/varsity spots, but I haven't necessarily seen an unusually high number of injuries or anything reckless about it. The same really good guys will still come out and if they are fit enough they will get the roster spots and make up a solid team because ultimately those guys are going to be at BYU either way.
Last example, one of my teammates in HS, who was a state XC champion in UT went to BYU. He had a bad summer before his freshman year and didn't make the cut. He never ran a single day as an official BYU team member and never even went to try out again. He stayed at BYU and graduated from there without any financial assistance. I don't think he ever even considered going to another school, though I'm sure he could have gotten a scholarship somewhere else.