So was this a legal or policy matter? If you were a PAP supporter you would go along with what Shanmugam said i.e., Parliament is sovereign and decided it was to be a reserved presidential elections. If you were anti-PAP then you would buy Sylvia Lim's argument that it had started out as a legal matter and then became a policy decision along the way.
This is how I would understand this:
Had Tan Cheng Bock not challenged this in court, it would be sold to Parliament and us as a legal sound and so Parliament is advised by ministers to take the legal advice on board. In this way the PAP government cannot be accused of being responsible for fixing the last PE to be a reserved one. Unfortunately for them Tan Cheng Bock mounted a challenge and this caused the government to give up its foil and admitted it was a policy matter. If this wasn't so, Tan Cheng Bock might have won in court.
This is yet another lesson why cannot afford to let the PAP dominate parliament without sufficient check on their power. Time and again they have not proven themselves to as honorable as claimed.
We must always treat this government with some suspicion because if you don't it might turn around and screw you. To illustrate, say between policy option A and B unlike in the distant past, politics is going to decide rather than the long term good. Assuming option A hurt you then better make a lot of noise hoping that those adversely affected by option B wouldn't. That is how issues will often be played.
Increasingly the PAP is becoming ordinary like politicians elsewhere. The journey to go from extraordinary to ordinary has begun. The best we can hope for is that they take this journey as slowly as possible. Perhaps along the way we will find much better people to run this place than this self serving group.
I thought Yahoo summarizes this quite well.
Update: October 5, 6:30am
And Mothership has done a very good job putting it all together but forgot to report the PSI number created by each minister.
When things are hazy you will have to just live with the oxymoron that these ministers have integrity with doubtful honesty. What I know is that as far back as I had complained about in 2011 you can't trust these guys without watching them to make sure they don't screw us, especially in order to serve the rich and powerful but most of all to stay in power regardless of their merit or lack of.