I think the Kensington lock is an absolutely waste. They've been around for decades on computers and I haven't seen one person use one nor have I. I bet if you took a poll on this forum of who has ever locked their device using the Kensington lock it would show zero have used one. The lack of a way to lock the Surface will not be something that is going to turn people off from buying a Surface.
Actually it has and will.
It many not deter consumers from buying the Surface for personal use, but it will be a roadblock to some corporate sales.
Our company looked at the original Surface Pro when it first came out and the lack of a convenient way to lock it was one of the reasons it wasn't adopted and why we decided to go with more laptops again even though there were many people who "liked" the Surface Pro. Lack of lock, plus lack of drivers to do a custom corporate image, no business class support, no TPM and on and on. Most have those issues have been resolved except still no Kensington lock and still no locking into a docking station except with the third party $200 metal housing.
There are many organizations that require that employees never walk away from a portable computing device not tethered or locked away.
So, the choice was to lock it in a cabinet every time you get up from your desk or carry it with you everywhere you go and both choices were more inconvenient than just using a Kensington lock with a regular laptop.