Microsoft seems to explain this approach with its desire to lower the power consumption of the devices, as well as with immature social network APIs. Whether that is the true reason, no one can be certain right now. At least we can hope the company will eventually add this functionality, should its products make a break through, as it intends to add more Windows Phone 7 code over time.
Speaking of power consumption, the batteries of both KINs will reportedly last about a weekend, which is actually something that has been targeted during the development phase. Well, if you ask us, having in mind these babies won't be able to push stuff to you, this doesn't really sound like a lot of time...
A disadvantage of the KIN ONE and TWO is their reported lack of microSD slot. While some wouldn't find this to be such an issue, given the devices' respective 4GB and 8GB internal memory, it might be a problem for others, who like to have tons of music with them all the time.
Microsoft KIN ONE Specifications
Microsoft KIN TWO Specifications
source: Engadget, more, more