To broaden this beyond "income level 4" (I'm using Hans Rosling's categorization system instead of First, second, third world), banning thimerosal has a huge impact on worldwide vaccination efforts. It's cheaper to supply multidose vials to lower income level places for numerous reasons, the major of which are: less packaging, and less infrastructure (refrigeration) required.
So it's not even a matter of "well if 'we' (read: those in the US, Europe, etc) don't really use/need it, why not just ban it anyways, just in case?" This is a common rebuttal to what you posted about the US not needing it due to the accessibility of refrigeration and speed with which vaccines are used, so it's very important to remind people they are not the only people on Earth. "We" aren't the only ones to consider. It's very difficult for people to grok the worldwide impact of selfish, fear-based, seemingly small decisions, but this is why people who want to rid the world of vaccine-preventable infections are so frustrated with the antivax conspiracies. It's not just an individual parent and their child in isolation. We live in a society. They are making decisions that impact everyone, and that's not hyperbole.
All that being said, it DOES have an impact on the level 4 countries that ban it in childhood vaccines. It makes them more expensive because they're single dose. Someone is ultimately paying that cost, be it taxpayers, insured folks, or private individuals.
And from WHO:
WHO policy is clear on this issue, and the Organization continues to recommend the use of vaccines containing thiomersal for global immunization programmes because the benefits of using such products far outweigh any theoretical risk of toxicity.
ETA: thiomersal is a synonym. Same stuff.
Naw, they already have those.