The reason for the differences may be that good presentations are much more important in biology. Even a mediocre talk will raise eyebrows, and it can kill your chances of getting a job. And a poorly written grant will not be funded, no matter how good the ideas. In biology there is a high overlap between people that do excellent research and give excellent presentations. Less so in mathematics. The cynical reply here is that these are just better salesman and get more funding, and hence run bigger and more productive labs. But perhaps these are simply the people who view the presentation of their research as an integral part of their work.I completely agree with Josic that presentations and communications are central to biological research, but here's why I think that is.
I'm not too familiar with the breadth of research subjects in mathematics, but in biological research, the topics are so diverse that you're pretty much guaranteed to be presenting to audiences where 90% of the members only have general grasp of your specific field, let alone the precise topic.
Thus, every presentation is a general primer on your topic and a lead-in to the problem you're trying to solve, why it is important to the field, and why it should be important to them.
The second aspect of learning how to present biological research is picked up in grad school; tailoring your presentations to your audience.
Given the same set of data, a presentation will be set up differently depending on whether it's a lab meeting, an advisory committee meeting, or a departmental meeting. Each of these groups has a specific need from you, which you must determine in advance and plan your presentation accordingly.
There are a ton of books on how to give great presentations: I liked Presentation Zen for it's reminders to keep slide clutter to a minimum; The Cognitive Style of Powerpoint by Edward Tufte for understanding visual communication; and more recently How To Give a TED Talk for advice on putting impact into your message.
Lastly, I wouldn't say calling biologists better salesmen is cynical; it's partly true. There's no shame in selling your science if you're trying to share a message with your audience (overselling your science is a different story). There's a little bit of salesmanship in every aspect of life, and research is no different.