If the consulting company you are looking at says "yes, we do that" to whatever technology you throw at them, they are probably learning on your dime. If you work for such a consulting company, you probably have a lot of sleepless nights and unhappy customers. A common truism is that no one can be an expert in everything and that extends to organizations as well. Highly sales focused organizations, in particular, can fall prey to this if the pressure to keep selling overwhelms the desire for quality delivery.
When I became the mobile practice lead early last year one of the first things my boss shared with me is that he wanted us to become a best in class provider for mobile services. In order to achieve that goal we had to decide what it is we actually do, and by extension what we don't do as well. Different companies may come to different conclusions but for our mobile practice we looked at our internal competencies, the spectrum of client needs and settled on native iOS/Android, Xamarin and Cordova, with responsive web applications being covered by other groups in the company. If a client needs Appcelerator of Kony development expertise we let them know that we may not be the best partner. This is in their best interest and in ours.
By deciding what we actually did in the mobile space we solved many problems. We now knew where to focus our training efforts and in so doing alleviated many delivery issues associated with resources that learn on the job. The impact of this keeps spreading. By reducing delivery issues our thought leadership becomes free to put more formalization around our technical delivery and ALM process, adding to our existing overall delivery process and in turn further reducing delivery issues associated with these processes. This again frees up management to work on other issues, including growing and scaling the business.
This idea isn't anything new. People can't be experts in everything and if they perpetually stay at the start of the learning curve of an overly wide variety of disciplines they will constantly be making the mistakes associated with that part of the curve; with management dealing with the fallout. As good consultants we don't do our clients any favors when we just blindly reply, "Yes, we do that" when we know it is far outside our our capabilities.
That's not to say you shouldn't move into new skill sets and product offerings as a person or as an organization. Indeed you likely need to do that to continue to thrive. But every new skill learned or product offered comes with a learning curve and a cost in terms of focus that is redirected into learning that skill set or creating that new product. With that in mind it should be a deliberate process, one where you understand and are prepared for the cost and with that understanding knowing that there is limited capability to do it all, know it all and learn it all at once.
To be best in class you need to limit the scope of that class to something that can be viably achieved and understand exactly what it is are best in class at. If you are on the other side and looking to hire a consulting company with best in class talent, just remember if they keep saying,"Yes we do that" to an overly wide variety of things, they probably are not best in class at anything and likely you will be paying them to learn.