While I agree that there could be some savings in WP.SE question height, I would say that it shouldn't be just as high.
The main reason is because SO and WP.SE are aimed at different audiences. SO is a purely developer-related SE site which has been around for a few years now. The target audience is tech-savvy IT-employees who are primarily looking for solutions to a problem. Due to the age and popularity of S0, a LOT of problems have already been answered, so users are encouraged to first look for existing answers before asking a question. Because of this, the question lists and overall layout are altered to show more questions on the same space.
WP.SE, on the other hand, is a site aimed at general employees looking for advice on problems they have with the workplace. This site doesn't yet have the userbase or snowball effect that SO has, so there's a good chance your question hasn't been asked (or answered) yet, or that similar issues are too different from yours. YOu are still encouraged to search first and ask questions afterwards, but due to the variations in workplaces, your question is likely to sufficiently different from existing ones.
In addition, your comparison image isn't quite accurate. It's not just the vertical height, but also the width AND the rest of the page. WP.SE has a lot more open room before the questions even start, with the questions starting about halfway down your image. The questions box is also narrower than on SO, because of the sidebar. This means that it's easier for questions to be long enough to not fit on 1 line, leading to less questions visible. The SO image is also 50 pixels higher, making the size comparison misleading in favor of SO.
In case of the frontpage, SO also has a larger focus on helping others. having more questions on the frontpage visible at once allows users to see more questions with their preferred tags without searching. WP.SE is more of a site that's visited on a daily basis, while SO is often visited on a hourly basis by programmers looking for answers.