Just an observation here, but...... Did an image search on the 280 and saw that it's a white-handle saw. Knowing that the 290 has an orange handle, it looked immediately like the 280 was part of the 'pro' line......which surprised me b/c I don't remember anything other than 260/360/440/460/660/880 in the last couple years (aside from the 1's and 2's on the end now).
I know that the white handle, at least in the last decade, has been a pretty good indicator of a Stihl 'pro' saw..........ya know, when you're looking at crappy pictures online and the model number isn't listed any where in the listing. But this got me puzzled, so I just went to Stihl-USA's website. Went to the mid-range area, 'Farm/Ranch'. Confirmed that the 290 still has the orange handle. But now all the 'new' saws in that range are white-handled....... 271/291/311/391. I haven't seen any of these revamped models in person yet, but assume they are still clamshell designs. I guess Stihl got away from delineating the clamshell design by putting an orange or black handle on it, versus the white on the pro saws.
I guess they're trying to make them all look like pro saws now, hoping they'll sell more