Creating a operating system for multithreaded apps is much harder compared to singelthreaded task based systems.

There would be some truth in the statement that WP is done to fit in slow hardware or hardware that need to take every step possible to save power TWO years ago. This is not the case anymore. At the end of 2012 we may see the first quad core mobile phone, we will certainly see it in 2013.

Also, threading done in the hardware does not consuming more power. Having two cores and you can lower the frequency to save power. Single core processor that his clocked high will consume more power compared to a dual core that has a bit lower frequency.
Mobile phones today is connected to internet all the time, they are checking things, tracking etc. All that while someone is talking in the phone or listens to music. In order to do that smoothly with a task based operating system it will consume much more power because the system needs to create all logic in the software.

Also Windows Phone will NEVER get same support for different types of hardware that linux has


Today if someone is saying "WP can't do multithreaded apps because it need to save power" is just marketing crap from someone that don't know how it works internally.