Murax bro i really didnt want to take part in this topic but now i feel like i must..
First of all, obedience to the ruler is wajib unless he comes with a clear cut kufr.. Him praying or not is not the only condition.. For example what if the ruler prays but commits shirk? Rafidas pray.. Also the salafi scholars differ on tarik salah(one who abandons prayer).. Shayk bin Baz says their kaffir while shayk Albani says no as long as he knows his sinning than his still a muslim..
There were many leaders who prayed and were seen performing Hajj yet some of the scholars made Takfiir on them due to their corrupt beliefs.. Saddam Hussien for example.. Shayk bin Baz said he was kaffir.. Khadafi also when he wrote his book (the green book) where he calls for the change of some ayats.. Saudi shayks have also made takfir on them..
Now what is clear cut kufr? There are many things and scholars have explained this..
One of them is shirk (associating partners with Allah).. Ruling by other than what Allah has revealed, meaning quran and sunnah.. Now when it comes to ruling by other than what Allah has revealed our salafi scholars of today say if the ruler rules by other than the Sharia but knows his sinning than his still a muslim but his a mujrim (criminal, sinner)who follows his desires... But if the ruler believes that sharia is backwards and Democracy or any of the men made laws are better than the sharia and are more befitting than that ruler is a Kafir by agreement of all Scholars..
Just to let you know here are some of the salafi scholars who have passed judgements against their rulers and gave fatwas to fight against them..
Shayk Il-islam ibn Taymiya faught against the tarters even though some of them prayed and said the shadaha because to him they were kaffirs due to their corrupt beliefs..
Imam Mohammud bin Abdulwahab waged Jihad against the Othmans because to him they have allowed shirk. That is how the kingdom of Saudi Arabia was established.

Makes you think ah?
P.S.. I agree with you in principle that the muslim rulers no matter how corrupt or evil they might be should not be rebelled against as long as their muslim..This is the way of the salafi.. but you will find that the issue in dispute in most cases is what takes a person out of islam.. My advice, we should all study the case more in detail..