Obviously you have not used a PIC, but I have used many of the 51 derivatives.

Compatible? The LPC9xx are not 5V, nor are the Silabs. Plenty of PICs run from 3 to 5V, even the 80 pin devices, so peripheral devices do not change if the processor changes.
Programming, the less said the better, the LPC9xx scared the hell out a lot of designers in India. Philips seems to change the programming algo nearly every time they change their chip vendor.
Most PICs have common programming tools. Microchip has free software tools(compiler, IDE) for the 18F, 30F and the newer devices, the 16F and 12F lack only a compiler from the company.
No Silab in DIP package, so difficult to give project to students and general prototyping.
Yes, I am comparing with whole list of companies you mention, except for TI and Philips who do give samples. But then again their distributors do not care to stock most of them. So the fact that 51 is the largest family is illusory in India.
Bugs, yes of course, PICs have them. And even in denial mode, if they know your competence level, they at most say "not able reproduce the bug", not question instead your ability to design.

I grew up on Intel and derivatives(8085, Z80 onwards) and with some exceptions, each chip family is created by competent engineers with some market segment in mind. So I would never be so rash in knocking down a family without really working with it and even then not in such terms.