'Target' rifles basically have more weight, better triggers, fully adjustable stocks ( usually with straighter pistol grips ) than a 'sporter' style gun.
Some will use them simply because they want to use the best available kit. Their money, so why not. Others will be very competitive and will want every possible advantage of getting as many targets down as possible.
The target guns are an obvious visual example of how the sport has moved on. It's the way that scopes have gone that is probably a bigger issue.
... with the quality of guns/scopes being used and the experience/quality of the top shooters courses are having to be tough to test the best ( most top comps now don't use many, if any, 40mm kills on prone shots etc ).
Many of course, with or without top end kit, will turn up to meet old friends and enjoy the social aspect. Attendances remain good and over 200 already booked for the Worlds 2014.