question about carbine front sight

[Doug.38PR]

http://www.rossiusa.com/product-details.cfm?id=158&category=8&toggle=&breadcrumbseries=
why do rossi versions have the front sight behind that barrel/tube ring

http://www.uberti.com/firearms/1873-rifle-and-carbine.php
and the uberti version has the front sight on top of the ring?

[Abilene]

Short answer: because that's the way Winchester made them. 

In your question, you have referenced two different models.  The '73's were made both ways, with earliest models having the sight integral with the barrel band.  Pictures I've seen of '92's had the sight on the barrel behind the band; don't know if they made those with the sight on the band, but it wouldn't surprise me.

There's some good pictures here: http://rarewinchesters.com/  Warning: drool on the keyboard can cause your computer to act up 

[Buck Stinson]

All first model 1873 carbines and some second models, had the front sight machined as part of the magazine tube band.   Around serial number 48,000, the 1873 carbine front sight was changed to the post just behind the front band.  All model 1892 carbines had the post style front sight, set just behind the front band.  Hope this will help.

Buck