Most of the larger suppliers have Flash but not all operators use them (preferring the download).
Then you have some smaller companies that only use Flash. for the most part I have found that there’s a huge gap in Flash versus Download with regards to quality, cohesion and playability which is strange considering that for the most part, Flash casino games are true cross platform compatible (barring some mobile devices *cough* Apple).
You’d think that there would be more quality Flash casinos out there.