I'm not arguing whether it's wrong or not - I said in another reply I can understand expecting compensation for one's time. I'm just saying it definitely adds pressure, and it seems there we are in agreement.
You're making a distinction without a difference. Sure, since removing shoes is less of a sacrifice than dropping 99k bells, more people would do it. But how
many people would feel pressured is not the point. The point is that we understand that phrase to be insinuating that you
ought to comply if you're a decent person. It definitely indicates the preference that you do what is "appreciated". That's the subtext of the phrase.
I think many people are not being honest with themselves about their motivations behind using the phrase. Imagine hosting and not a single person leaves you a tip. Would you truly be fine with that, or would you feel bitter? Many, I'm sure, if they're being honest with themselves, would feel bitter. That doesn't make you a bad person. But it means you're mentioning tips because you're trying to subtly remind people to give them because you want them and expect them.
And if you are one of the few who genuinely means it and who would honestly be fine if you got no tips? Then perhaps you should follow the
advice @Mairen and
@lackless gave, because you are earnestly misunderstanding the effect the phrase has on your audience.