...you cannot exclude this possibility...
Agree, and from the statements of the investigation commitee so far, it has not been ruled out yet (or we don't know about it). However there is nothing at the moment that would explicitely point towards such a possibility as likely.
Don't forget the poitics of the investigation (let's face it, in both Polish and Russian cultures, appropriating blame is as important - if not more so - as finding out what happened):
- The Russian's interest is clearly to demonstrate that all navaids functioned properly, ground control did all the appropriate things, and the (Russian bulit) plane was technically sound. However if there is a choice, a technical problem on the aircraft would still be more 'favorable', as there the blame can possibly be shared with those who maintained and operated it.
- The Poles interest is clearly the opposite, to demonstrate that the pilot made all the right choices, some unavoidable external factor caused the event.
If you look at the opposing interests, probably a technical malfunction of the plane would leave the least red faces among the persons affected. Were that a likely case, I'm sure it would be already wide accross the press, even if in a speculative manner.