NMS shares can trade on any exchange, but there is still a primary listing exchange. They're mainly (AIUI) responsible for publishing data on various administrative minutia such as the handling of dividends and splits. I imagine most of LTSE's attraction to companies is enhancing the perception of only accepting listings from companies with a long-term view

Much like as an investor you'd think twice before purchasing an OTCBB share today, or perhaps 30 years ago pay more attention to the difference in listing requirements between Nasdaq and NYSE, I think that's what's intended here