Programmers often serves as a designer of user interfaces. You could argue whether it is good or not. However, especially in small companies, it is a reality that does not change.
What do you think personally as a programmer, is it our work to design UI? Personally I think that not, especially when you are going to work on Web Applications, where they made you to design UI also.
****Correct me if I am wrong.****
In an ideal world there should be a UI designer, just as there should be a DB designer, etc.
However, this would mean that even the shortest projects run by the smallest companies would need a team of at least 3 (or more) people. Because of the cost that this would incur it's never going to happen.
On small projects you are going to have to double up job functions in fewer people. It's a fact of life.
From a pragmatic point of view I think that all programmers should have an understanding of the basics of UI design, if only to be able to spot a bad one and do something about it. I also think that programmers should have an understanding of DB design as well.
You should look on this as an extra skill set you have which will give you more options when looking for new career opportunities in the future.