They are following certain guidelines laid out by expert
committees on the way a disease should be managed. Ordering
unnecessary tests does happen, but it is not to earn money, but to
protect the doctor's backside. Without lab tests, doctors have to
rely on their clinical skills and experience to make decisions. All
the responsibility falls on them. Sometimes they make a bad
decision and they can be sued. On the other hand, even if you make
a bad call based on an erroneous lab result, you can blame it on
the tests results and the lab.
Most patients are subsidized patients anyway, and unless you are a
private patient, the hospital actually loses money on lab tests.
The government provides a fixed subvention for subsidized patients
and if you use it up on unnecessary lab tests and go into deficit,
the hospital has to pick up the tab.
You can only earn money on the private patients. So if the
intention is to earn money on lab tests, what will happen is that
they overservice the private patients and deny subsidized patients
even necessary tests. I don't think that is the case because
doctors are afraid of being sued, and it is more likely that they
would overservice patients just so that they cannot be blamed if
something goes wrong. Therefore I really think the reason for
unnecessary tests is because doctors don't want to be sued...they
want to protect their backsides. I know that is true because I have
done it myself 
By the way, hospitals earn more money on operations rather than lab
tests. That is why they are outsourcing X-rays and other tests to
India...to cut their overheads and increase their margins. If we
can earn so much from diagnostic tests, why are we so keen to send
them away? No, the fact is that we lose money from these
tests.
If doctors want to please their administrators, they will do more
cosmetic surgery, put in breast implants and do laser keratoplasty
(for shortsightedness), not order more lab tests.
BTW, I didn't realize that polyclinics charge more for lab tests
than TTSH.....most polyclinic lab services are outsourced to
private labs. If TTSH labs can do it motre cheaply, I cannot
understand why they continue to outsource the service
either...