This raises a good point which, IMO, validates once again actual Bible principles vs the WT interpretation and implementation of them.
The Bible makes it clear that it is the underlying materialism itself - not the valuable objects - that are the problem. In doing so, it encourages Christians to actually go to the root of the issue and deal with it there. If you do not desire these things in the first place, then you won't be put in a compromising situation.
Now look at the GB. They become caught in the following dilemma while recommending others should "keep your eye simple" and not pursue "material things":
1) You purchase expensive items for yourself because you desire them.
Do you wear/use them while preaching to the "flock" live or on broadcasts? If so, you appear at best insensitive to the relative poverty of your followers, and at worst, a hypocrite.
Do you decide NOT to wear/use them while preaching so as not to offend others? Then again, you appear a hypocrite. If you are seen wearing/using items you are not prepared to wear/use in front of followers, people will inevitably ask "why?"
2) You are given expensive items as gifts and keep them for yourself because you desire them.
Do you wear/use them? If so, you again risk appearing greedy and hypocritical. People will rightly wonder why such items haven't been "donated" for the worldwide work, as many others are expected to do with their "valuable things".
Either way, choosing to wear/use such items any time, wherever they came from, compromises your position.
What if you decide to keep the valuable items without wearing/using them? What's the point? What motive would you have except to take them out sometimes and gloat over the fact you have them? Would it not be better to sell them if you are not going to use them for the purpose they are intended?
There are also other risks. Having those expensive items around you becomes all about image and vanity. It also means you become afraid of losing them, perhaps to the extent of being mentally dependent on having them. Like Gollum with his "precious" ring!
So if you are supposed to be advocates for "keeping your eye simple", the only solution to putting yourself in that situation is to take the original scriptural line and not desire what is materially excessive in the first place. As WingCommander said, you can wear a watch that does the job and still has a good inherent value without it being a massively expensive status symbol. Likewise with the kind of clothes you wear, car you drive, and so on.
As Tonus added, it's about the motive and the example you set (two things which again, they are constantly counselling the R&F about) and it always looks bad when the GB appear like this while promoting "self-sacrifice" and "modesty" and showing pictures of the elderly and little children putting their last pennies in a contribution box.