PHP based exchanges are very much fake valuations
What does this have to do with the programming language the exchange is written in?
Correct, one thing has nothing to do with the other.
First of all, exchanges don't even provide 'valuations', they provide market prices based on order flow.
As others pointed out, it is impossible for exchanges to manipulate prices for very long because of arbitrage.
If an exchange artificially lowers price, they do it to their own detriment because traders will buy it cheap from them and sell elsewhere. If they artificially raise price, they lose money in the same fashion as traders buy from other exchanges and dump them at a premium. The only exceptions I can think of are a ridiculously large spread, or a gox situation where you can't get your money out; that's a different story.
As for PHP, there is nothing wrong with it per se. There are many wonderful MVC PHP frameworks available which make front end development robust. It may not be ideal for the backend of a large scale trading engine, but even that depends on the database and the overall architecture of the system.
also, folks should stop pretending/assuming they know the architecture of someone else's website when they don't.
