You mention our friends at LimeSharp, but I guess as we get more and more attention, you’ll find more and more people explicitly pitching MODx at clients. You sure have noticed it’s a strategic choice for LimeSharp, they also pitch KnowledgeTree, LimeMail and CubeCart. Right now, not many people (to my knowledge) have chosen to do so.
Being specialized in a given solution has its pros and cons.
Pros : If a client already knows that he wants MODx for his website (or that MODx is in its shortlist), he’ll most definitely choose someone based on his knowledge and experience building websites with it (that plus checking out his previous work of course). As time goes by and your MODx portfolio grows, you’ll dig a position in the MODx specialist sub-market. And that’s good if MODx reputation continues to spread. In a way, choosing this strategy is betting on MODx success
Cons: If you’re a small webdesign/development business, more likely than not most of your work is small/medium businesses too. It means, more often than not, that the would-be client has no idea what he wants or at least no clear idea - and he sure does not know a lot about CMSes, the benefits of webstandards or accessibility. Most of what is knows is tied to what he saw on the web (and liked) and what his/her friend told them about the software they’re using for their company. Pitching MODx explicitly does not help your selling websites. It might be that your prospect wonders if a single solution can fit all needs and if you’re not trying to fit your solutions into his needs.
I don’t know about you, but as far as I am concerned the way I went about selling my services is : translate into layman terms what is great about modern webdesign and web applications. What it means to them.
XHTML, CSS ? Might mean something to you but your client won’t care really. What he wants to know is that the choice he makes today are the best way to reduce development and maintenance cost thanks to the separation of content and presentation (a concept he will understand), to guarantee that he will be able to have his website displayed on a PDA or phone, that old or disabled people will be able to change font size or click on menu items, etc...
MODx ? Hmmmm, I sure am a big advertiser for it but it’s not what I start with.
I start with the concept behind the tool : flexibility (you’re not locked into a pattern), modularity (by splitting content into manageable sized chunks, I work faster and maitenance is easier), scalability (you want to evolve ? well you have a framework to build upon) and user friendliness (a quickedit demo is worth a thousand words

and even though it still suffers from shortcomings, clients like the MODx admin).
Then I mention MODx as a tool and why it fits all of the above. I talk about the guys behing the tool, the fact that it’s experienced people behind the wheel. That there is an extended dev team, a tester team. Of course I mention the cutting edge technology, the community and open source benefits. Then I show some sample websites, that you can do whatever you want in terms of design.
My strategy is somewhat of a funnel : I start wide and finish narrow.
Kind of the opposite of what LimeSharp does : start narrow (MODx) and go wide (client benefits).
Of course, things will change with MODx new core. We’re one step up with MODx become a full blown web application framework. Marketing will have to adjust to the new capabilities and possibly new positionning (against RoR, Django... etc ? We’ll see).