I really don't foresee hordes of elderly walking home from clinics, actually. Just saying.
That first statement's rather absolute, isn't it? There are many more factors than just "corruptible or not". Even corruptibility has different degrees. I would go so far as to say that everyone possibly has his price, and it may not be in terms of money - but having a high pay probably does play a role (not clear how significant though) in dissuading corruption in the form of bribery. Putting it into a rather simplistic framework - the choice a highly paid person faces when say, he is offered a bribe is going to be rather different from a person receiving less pay:
Highly paid person faces the choice of (A) Taking the bribe and risking losing his high pay if discovered; or (B) Rejecting the bribe and being sure of continuing his high pay. When you substitute a high pay for something less, then the choice becomes blurrer, doesn't it - and if you push it to the extreme and pay him nothing at all (claiming that he will get an extremely pleasant warm fuzzy feeling in his heart by doing public service) then you can see why B becomes a rather more attractive choice.
This probably also answers your next question somewhat. I think the underlying idea of high pay in Singapore isn't "let's attract the money-minded". It tends more towards the "let's get the people who want to serve, and make sure that they aren't tempted to err". It's of course debateable (which is why ministerial pay is so often debated publicly and privately) how much you should pay to lower the chances of temptation but I think it is a little warped to say that waving high ministerial pay only results in money-motivated individuals coming forward. That's certainly not true as a Minister's job doesn't involve just stepping forward to collect pay, it also involves a lot of other things like being thrust into severe and critical public scrutiny, some amount of commitment in terms of time and responsibility.