For those who encountered the same issue (when you try to access the element using xpath by the node name in Eclipse built-in parser) I would recommend either to remove namespace definition from the document at all or remove the default namespace.
Example:
<apprepo xmlns="asdasd">
<app name="good-app">
<appinfo>
<author name="John Smith"/>
<stores>
<store name="goo" price="1"/>
<store name="app" price="1.5"/>
</stores>
</appinfo>
</app>
<app name="another-good-app">
<appinfo>
<author name="James Smith"/>
<stores>
<store name="goo" price="2"/>
</stores>
</appinfo>
</app>
</apprepo>
Query: //appinfo returns "no matches"
Let's now change the namespace so that it is bound to some prefix (let's even not use that prefix in our document)
<apprepo xmlns:pref="asdasd">
<app name="good-app">
<appinfo>
<author name="John Smith"/>
<stores>
<store name="goo" price="1"/>
<store name="app" price="1.5"/>
</stores>
</appinfo>
</app>
<app name="another-good-app">
<appinfo>
<author name="James Smith"/>
<stores>
<store name="goo" price="2"/>
</stores>
</appinfo>
</app>
</apprepo>
Example:
<apprepo xmlns="asdasd">
<app name="good-app">
<appinfo>
<author name="John Smith"/>
<stores>
<store name="goo" price="1"/>
<store name="app" price="1.5"/>
</stores>
</appinfo>
</app>
<app name="another-good-app">
<appinfo>
<author name="James Smith"/>
<stores>
<store name="goo" price="2"/>
</stores>
</appinfo>
</app>
</apprepo>
Query: //appinfo returns "no matches"
Let's now change the namespace so that it is bound to some prefix (let's even not use that prefix in our document)
<apprepo xmlns:pref="asdasd">
<app name="good-app">
<appinfo>
<author name="John Smith"/>
<stores>
<store name="goo" price="1"/>
<store name="app" price="1.5"/>
</stores>
</appinfo>
</app>
<app name="another-good-app">
<appinfo>
<author name="James Smith"/>
<stores>
<store name="goo" price="2"/>
</stores>
</appinfo>
</app>
</apprepo>
Result: query returns all the appinfo nodes found
P.S. - the proper parsing happens even if you completely get rid of the namespace attribute. So Eclipse xpath parser is not working with the documents having the default namespace set.