i think that the reason guns like you mention in 300RUM, 30-06, 270 eor whatever are sightless, is because they are by design long range cartridges, which unless you have a 30"+ barrel and receiver or tang sight for a very long sighting radius, you will need to use a scope to max their potential out to the ranges they were intended to be used at. If you want a short range bush gun there are lots out there that have open sights but they are typically chambered in short to moderate range cartridges that do not require the use of a scope to be accurate within their intended effective range. 45/70, .450, .444, 35 rem, 30-30... these are rifles that absolutely must come with open sights.
Now if marlin stopped equiping their guns with sights... there would be a real issue. But really, why in the hell would anybody want a .300RUM in a short range gun?