Tubeless tyres are self-sealing - compared to tubed and to a limited extent. Manufacturers have chosen to go the no-spare route for two reasons. Firstly, carrying less weight improves mpg, slightly. Secondly, their data presumably suggest that punctures are not too much of a problem for most people. Tubed tyres tend to not to deflate suddenly, as tubed ones do, because of their slight self-sealing attributes.
People who check their tyres regularly and are (I was going to say normally but perhaps not...) observant tend to pick up tyre problems before they become serious. Blowouts are rare (more on that shortly) and you will probably be concerned with other things if that occurs.
The only place where blowouts may be wrongly uncredited is motorway accidents. It seems to me that continuous high speed on poorly (if at all) maintained tyres would be a source of accidents but it is difficult to obtain data. There does seem to be a large number of "unexplained" crossover/lane swapping accidents on motorways, though. High speed tyre failure would seem to be a likely candidate for the cause of them.
If you really have a high number of punctures to deal with, have you tried any of the sealing gunks on the market?
