1. It's not difficult to customize Windows. There are well defined SDKs and interfaces for most of the kernel points. Honestly, how many web startups are custom

1. It's not difficult to customize Windows. There are well defined SDKs and interfaces for most of the kernel points. Honestly, how many web startups are customizing their kernel? 3. The performance differences are negligible in the general case. Startups write their own code so most of the performance differences are going to come from the code they write rather than underlying performance differences. In both cases, python vs. C# / .NET you can always drop down to C. I doubt that whatever their problems are they stem from language / compiler. Most sites are IO bound. IO bound applications are largely a factor of how many disks you have. The throughput for writing a file in PHP and C are identical on machines with less than 10 disks. 4. Licensing costs decrease drastically as you scale on the MSFT side.