Quo Vadis Professional Certification in Documentation

Wondering if the current categorization of course diversification is really required as some of these certification institutes, even some universities, seem to be churning out a never-ending spiral of specialization that end up in propagating the same information that is inherently taught in the other courses or should be a part of a super set group.
I will not put any particular certification to test but without some example my concern may not be clear, and of course I do not expect your agreement with my ideas but just provide some food for thought.
Technical Writing, for example, would require skills in language and computer applications, and this same skill set is required for Instructional Design. Each one may require a specific domain knowledge and that is true for almost all professions and depends on a job profile in a particular company.
To make the context clearer, let us qualify that technical writing would require knowledge of English (just for this instance as my ramblings are in this language) and a degree in Education. Technical writers are nothing but educators, especially of a specific computer application or platform, and so are instructional designers, except that they may deal with a different subject matter but the education media would be computers. Essentially they are doing the same task of educating by using of the same electronic media and thus having the same skill set requirement. Yet we see a pseudo-differentiation as technical writers and instructional designers.
Instructional designers are often required to know educational models like, Behaviourist, Cognitivist, Constructivist, etc. Can technical writers be really successful in their objective of imparting knowledge that will be comprehendable if they are unaware of education methodologies? They cannot do away with educational theories if they are serious about their profession. So essentially they belong to the same super set of computer based educators. Classifying them into two water tight groups is like categorizing junior school teachers (excluding primary teachers) and senior school teacher as two separate classes of teachers who cannot function in each others domain.
Why then do we perceive technical writer as different form instructional designer? Is it because these groups get marketed as such by a third party whose business is to create certification courses and ensure they do not run out of business? Would I say a programmer who can only write codes are different from those who can can also store them in version control application or take part in configuration management to be different from each other? I would rather say the latter group or groups are the programmers with an extra set of skills but that still makes them programmers.
A technical writer with language skills and a background in education has a good standing in documentation. This background makes them a good instructional designer as well. So essentially they are both good documentation specialists. How incongruous does it look to have a company advertise for technical writers and instructional designer separately as if they are different professionals. Would it not be better to seek documentation specialists with skills in technical writing and instructional designing, just as we seek for skills in HTML, XML, SCORM, DITA, etc., or experience in one specific domain, rather than categorize a true group into perceived categories that may not stand the test of classification by exclusion.
In my experience as technical writer I have often had to create CBT and WBT, as another instructional designer may have ended up writing white papers and manuals. This is simply because both these groups fall under documentation specialist that a company has at its disposal often named as one or the other. I have even been into marketing communications while holding the job title of technical writer, because often companies do not have specialist with that job title or the technical writer may be best suited SME for a particular application. The company is aware that essentially these job titles and profile classifications do not fall into water tight compartments. Once we know what we are dealing with, this only raises the question if the HR of the company is really aware of what it seeks.
I am not contesting specialization courses that groom a professional in a particular set of skills but just highlighting the fact that technical writing, instructional design, marketing communications, etc., are essentially the same. Specializing in Human Resource or Marketing, while studying management makes one a management professional with a specialization in that area not a separate professional with a different degree. Its high time the institutes catering to separate technical writing and instruction designing courses realize what they are into, rather than create a poor impression about itself in the industry that knows what is required to do the job.