There are lots of reasons for a dog to have a low PLT count.. Anaplasma-Erlicia.. and other tick dieases can be a common cause, also Auto immune issues, and some forms of cancer..bleeding disorders.. and this is the "short" list..
So you know.. Bone cancer can cause a fracture.. but generally Not PLT problems.. also in "most" not all Fracture cases a very obvious bone lesion is visiable on a x-ray and a vet can see that the tumor weakend the bone.. Bone cancer is very common in this breed.. but so are fractures of the more normal sort.. Any fracture can lower the PLT count if there is signifigant trauma and hemmorage too.. this may be the case.. but one MUST test further to find out.. a low PLT due to trauma hemmorage, looks the same on a baseline CBC as one with a more serious cause..
Most of these tests to determine/rule out causes.. DO take several days to get results.. it is not a money ploy.. unfortunaly many of the tick panels.. and diagnostic testing is also expensive.. also there is a list of causes.. that one MUST rule out.. to ensure that you are not dealing with a more serious systemic problem..
If the dog has a PLT problem, of any cause.. the surgery would not be a good idea..the dog could bleed out..and die.. the fracture can be splinted short term and surgery done at a later date AFTER the dog is stable enough for the surgery.. It seems like your vet is being prety carefull.. doing pre surgery testing..I know of Many would have not required or done Bloodowork to "save" the owner money..if they offered the option to you GOOD for you.. this is why vets recommend it!!!
Now.. They did ID a potential problem..now the tricky part is figuring out why.. Low PLT issues are difficult to nail down.. find easy.. finding a specific cause not so easy = Testing.. and lots of testing.. but that is the truth of the matter..
But if you are not happy.. how about a second opinion? always a option..