curious There are some key differences in two regards: One, the US two-party system means that the largest party automatically has a full majority. Second, the office plays a much more partisan role. I am not too familiar with the formal rules and responsibilities for either office, but the way I understand it, both are primarily tasked with guarding procedure, but the Speaker is a lot more likely to wield his powers in a partisan way than the president of the Bundestag is. That makes the party affiliation of the president of the Bundestag mostly a formality, whereas the Speaker's can affect the way the House is run. For an even more non-partisan parliamentary head, see the Speaker of the House of Commons in Britain, who upon election renounces his party membership and only votes according to a predefined formula.
In Germany, there have been several cases where the largest party was not part of the majority coalition, but still had the office of Bundestagspräsident.