Is it common for Series A funders to get first right to Series B

It is not uncommon - but it isn't an "attraction" so much as a term they will include if it is their process. If it is important to them and they are making an investment, then it will be in the term sheet. If they are not making an investment and you offer it, it will make zero difference.

This is different than the pro rata rights nearly all investors will demand. In neither case does it obligate them to make a further investment.

If you are talking about pro-rata rights ( the right to participate in a subsequent round of funding to maintain their level of percentage ownership in the company ), then yes this is quite common.