I believe, the original answer hasn't really been answered yet, which was, why there's no `bounds` element in the XAPI response. So, let's take a closer look.
After all, the XAPI call to the following URL will be translated into something Overpass API can make some sense out of, notably an Overpass XML request.
You, if you query for
overpass.osm.rambler.ru/cgi/xapi_meta?*[bbox=27.9314,-26.1841,28.1538,-26.0028]
this will in fact be translated into the following Overpass XML query:
<query type="node">
<bbox-query s="-26.1841" n="-26.0028" w="27.9314" e="28.1538"/>
</query>
<union>
<item/>
<query type="way">
<bbox-query s="-26.1841" n="-26.0028" w="27.9314" e="28.1538"/>
</query>
<recurse type="way-node"/>
</union>
<print mode="meta"/>
<query type="relation">
<bbox-query s="-26.1841" n="-26.0028" w="27.9314" e="28.1538"/>
</query>
<print mode="meta"/>
BTW: You can get to this translated query on your own, if you're following the [XAPI Compatibility Layer to Overpass XML / QL migration procedure, as outlined in the wiki][1].
That's already a good starting point to feed into overpass turbo: http://overpass-turbo.eu/s/eAf
So how do we get the bounds element into this?
You need to know that this requires something called global bounding box, which can be added by providing an <osm_script> element along with a bbox. You're Your resulting query looks like this: it's basically the same overpass turbo query as your xapi_meta call, before, but this time with also returning a `bounds` element.
http://overpass-turbo.eu/s/eAh
Once you export it You can get the query results from overpass turbo via Export -> get raw data directly from Overpass API, you'll end up with a file called interpreter and the following line in the resulting file:
<bounds minlat="-26.1841" minlon="27.9314" maxlat="-26.0028" maxlon="28.1538"/>
Missing accomplished!
[1]: http://wiki.openstreetmap.org/wiki/Overpass_API/XAPI_Compatibility_Layer#Migrating_from_XAPI_Compatibility_Layer_to_Overpass_XML_.2F_QL
