To some extent folks adopt their software development specialization depending upon their own skills and tastes: do they feel more comfortable with a broader and lighter background or do they prefer to be deeper and more focused? Managers may also have a strong influence over how employees develop their skills simply by the tone and expectations that they set.
Obviously software development requires some specialization, since the technological complexity and the rate of change in our profession precludes a sole person from spending the time required to be a technical expert at all the myriad skills that span the available range of tools. If you wish to employ an expert a direct corollary will be that you therefore choose a specialist. If you plant a honeysuckle tree, you are going to get hummingbirds: that's the sort of specialist this tree desires.
Selecting specialists for software development presents some challenging issues. Unlike hiring engineers to design cars -- where once the model rolls off the production line the engineers move along to their next project -- hiring engineers for a software project is likely hiring them for the entire life of the system.
In this instance the problem that a manager faces is that quality, job security, and concurrency are in opposition. Asking your staff to specialize may give them greater job security and improve the quality of your operations, but they will lose their awareness of how to incorporate and apply new tools and hence lose their personal marketability.
If you hire a specialist to do the job then the result is going to be somewhat unmaintainable by anyone but that specialist. If you hire a generalist it will be far easier to maintain the resultant system, although the final product may well appear less slick and polished.
Ultimately then who you hire depends upon the "positioning" your company is trying to achieve. Are they looking for a short-lasting expensive best of breed solution? Or something long term, stable, and adequate? What sort of tree exactly are you planting?