Do you think it's rude for the host of a get-together to ask that attendees bring specific dishes?

If the host of a potluck doesn't specify certain dishes everyone could show up with the same thing. So I don't see this as rude unless the message was delivered rudely. But it's not a problem to say, "The turkey, gravy and stuffing is covered so please bring a side dish".

It actually makes sense for people to be asked to bring specific dishes, if they can cook them successfully.  That way, there won't be duplications of one thing, and something else will be left out. 

At celebrations such as Thanksgiving and Christmas, it is not unusual for the host/hostess to ask their guests to bring along a specific dish.  People often like to contribute to the celebrations and will be happy to accommodate the host/hostess' request.  Equally, some people can become territorial about a certain dish and only want to contribute if they can bring along what they see as their speciality.  Other people may be totally put out by being asked to contribute, if they hold an expectation that the host/hostess will provide the entire meal.  Ultimately, the host/hostess will decide who to ask, if anyone, and the guests will decide if they wish to contribute.  There is no one golden rule.

nothing wrong with asking others to bring a dish. I do it all the time when I have a get together with friends. they also ask me all the time to bring a dish also

Normally, the hostess would supply the food. Maybe there are some instances where people might bring things. In that case, have a sign up sheet. The hostess can list what she wants, and then guests can choose from the list.

Good question!   The gen'l rule of thumb (fam and/or friends) is that the host has a right to issue general requests, like side dish, salad, pie, etc.  But it's being a bit cheeky to ask for a specific dish.  If a person wants that much control over the menu, she should just ask people to bring beverages and do the cooking herself.

That said, when it comes to family or close friends, the dynamics and tradition matter most.   My sister hosts all of my fam's stuff and she just asks us what we're bringing.   If we end up with no pies or sweet potatoes, she takes care of that herself.  She likes being surprised, seriously!  With my husband's parents, I always ask what she needs and sometimes she'll beg (lol) for a specific salad I make.  It doesn't bother me, because we're super close.  She pays for the ingredients, though, because we fly cross country to be with them and she insists. 

It sounds to me as if people are miffed not at the idea of coordinating the dishes, but the categoric way you seem to be handing out the tasks. You should all be talking about this together, not having one person say 'Hilda, salad; Millie, green beans and garlic; Janie, you're on pasta sauce'  etc.

I would instead say, 'Millie, Janie, I wondered if the two of you could be in charge of the salads?'

EDIT to add: Sorry, I misread the question. I thought YOU were the person issuing the orders.

i dont think so

No, I don't think planning a menu and asking everyone to contribute a part of that menu is rude.  It is rational.  Of course, it is polite to as the participants if they are comfortable provided a particular dish and to also try to make the cost equitable.

Not rude, especially among family.  Like you say, you don't want to end up with 4 pumpkin pie deserts and not potatoes, etc.

But to save people's feelings, family should know by now if someone has a specialty that they tend to bring, and have a bit of a discussion.  Then again, you might end up with 4 specialty pumpkin pies.