Both focus on practice and study. What you're probably noticing is that the Theravadins one encounters online, most of whom are Western converts, tend to have a different attitude towards scripture than Buddhists generally. While it's true that Theravadins have a different view of scripture on the whole (as well as what counts as scripture), I don't think it's something that monks of the different traditions argue about when they meet. But what I think happens is that in the West Theravada attracts more converts of a particular mindset—i.e. with a particular attitude towards the importance of scriptural fidelity—which skews the sample considerably and doesn't necessarily reflect a difference between the traditions as a whole. A lot of that comes from converts' treating the Pali Canon as if it were the Bible.
Another thing that skews the sample is the fact that online people aren't practicing but discussing doctrinal things, so if you've never met Theravadins outside of the Internet, you might come to think that all they do is talk about scriptures. Or that they study before they practice, or in lieu of practice. I don't think that's true. All forms of Buddhism are centered on practice, with scriptures and doctrines as supplements to help along the way.
And let us not forget that, while practice groups will get you practicing first so that you'll have a better context for the scriptural study, Mahayana has a much larger canon of scriptures overall, some of which have received literal worship over the centuries. And the specifically Mahayana sutras talk at length about how meritorious it is to recite, copy, and expound on them.
Now, as for whether Theravadins have traditionally gone in for holding lay retreats and getting laymen practicing hard the way Mahayana schools do, I really don't know. But I suspect that in the West people of a Theravada bent aren't going to be content watching the monks do all the meditation practice. And the methods are actually very similar, even if Mahayana contains a wider diversity of methods.
Indeed, I would say that diversity is the main difference. There's diversity in the world of Theravada, but the Mahayana tradition has been much less hesitant to embrace a wide diversity of practices and skillful means in order to get everyone walking the Buddha path.
