My android tablet will play flash, yet the site still redirects to the Google play store. You can go to many websites that use flash but not get redirected. This is just how the set things up. If you come on a tablet, you get redirected to the app they want you to use.
I've just checked this for you, it's because the itv Internet site uses flash, PC's can the iPad however cannot use flash, it diverts you to the app as this plays all itv programmes bypassing the use of flash.
I hope this answers your question.