I will keep this short and simple.
Of the two examples you have given, only one makes sense for search. I will explain.
- Las Vegas Plumbers
- Plumbers in Las Vegas
Search engines use semantic analysis to understand content or pieces of content. Those who know me will say, "Yes. Of course." and will recognize this answer.
I like to ask the question, "What about...?" What about Las Vegas Plumbers? There is no answer here. It is incomplete. However, is Plumbers in Las Vegas more complete?
The answer is a resounding, Yes!
While there does not seem to be a difference, there actually is a huge difference. Every sentence has one or more subject, predicate, and object that defines the base understanding of content. For example, Sally threw the ball is a complete sentence and a complete representation of subject, predicate, and object. Sally is the subject. Threw is the predicate. And Ball is the object. Without going through more complex examples, afterall I have covered this elsewhere, Plumbers in Las Vegas is also a complete representation of subject, predicate, and object. Plumbers is the subject. In is the predicate. And Las Vegas is the object.
Keep in mind that Google, and likely Bing, applies semantics on both ends of the process. Content is not indexed as a string of terms, but as semantic representations of the content using more than one application of semantic analysis (algorithm). As well, the search query is analyzed the same way. Early on, Google recognized that there were special search queries that occur most often. While it is not necessary to recognize this specifically, special attention was paid to these queries early on. One of which is service in location. For example, Chinese Restaurant in Chicago. Again, Restaurant is the subject. Chinese is a modifier of the subject to distinguish what kind of restaurant. In is the predicate. And finally, Chicago is the object.
Since special attention is paid to certain queries and semantic analysis applied within the index, fact links are used. For example, a web site for a Chinese restaurant lists it's location. It is in Chicago. Fact links relate subject, predicate, and object. Restaurant is linked to the modifier Chinese as well as being linked to location such as Chicago. More fact links make the location more specific. A simple query can retrieve all restaurants in Chicago without specifically and directly referencing content as a textual string. The index is data that can be queried directly as like in any database.
Your last example is the only one that makes sense knowing how search works and knowing how people use search. It is a complete representation that includes a subject, predicate, and object that allows for a direct query to the index for accurate and relevant results. Without this representation, the query falls back to simple term searches that Google states in is original research paper as yielding poor results. Why? Because there is no context to the terms being searched for. Remember my question, "What about...?"