Thats interesting because every single car that I have had be it company or private, Ford, BMW, Alfa, Mazda, Peugeot, Renault, VW, Audi, Honda... I have always had serviced on a Saturday. My current MX5 had the big 3.5 hour service done on a Saturday morning last year.
However you have made a very good point regarding independents. I have a friend of mine who owns a family garage, MOT and service centre it has been operating since 1960. I may as well get them to do the servicing work as they looked after my Volvo for 5 years perfectly and my mothers cars. The Lexus stamp is not going to make the blindest difference to value when I sell it in 3 years time - it will be pretty much worthless then anyway.
When I next get a nearly new one I will keep that maintained at Lexus themselves until it reaches a high mileage.