To add a little to what Sean has said, I offer the following thoughts on where I think the problem lies all too often with newbiew to spey casting.
When someone who has never fly fished before asks an experienced fly fisher or walks into a fly shop and asks the folks working in the shop to help him get started fly fishing, the first things the shop or experienced fly fisher asked are: What fish is going to be fished for? and What size water is going to be fished? After this infor is provided by the newcomer, we make our recommendation of rod length and line wt. However, I don't know anyone who would recommend a person that is new to fly fishing buy a "steelhead/salmon taper", or any other of the WF single-hand lines with belly/backtapers of 50'+ because we know such a line would end up frustrating the new caster. Instead, we recommend the newcomer get a WF floating line to match the rod's line rating.
The same ought to be applied to newcomers to spey. The long-belly spey lines with their 75'-100' bellies are analogous to the steelhead/salmon or distance tapers with their 50-65' bellies of the single-hand world and as such, they should never be recommended to a newcomer anymore than a steelhead/salmon taper is recommended to a new single-hand fly fisher.
Likewise, we wouldn't recommend a shooting head/taper to a newcomer to single-hand fly fishing because it is a specialized line that comes into its own in the hands of experienced and good fly casters. Therefore, since a single-hand shooting head is analogous to the Skagit and Scando lines, they would not be the best recommendation for a new, inexperienced spey caster.
Since we would recommend a WF single-hand line with its 30' belly to a new single-hand fly caster. Since the short-belly spey lines are analogous to the standard 30' belly WF single-hand line, a logical recommendation for a newcomer to spey casting is one of the short-belly spey lines with their 48'-55' bellies in the appropriate size for the rod's line rating.
And because one of the slightly longer belly WF single-hand lines line the Wulff Triangle Taper with its 38'-40' belly or the RIO Windcutter single-hand line with its 42' or so belly is not so much longer than the standard 30' belly WF line, one of them could also be used by a new fly caster with only a modicum of extra difficulty compared to the standard 30' WF single-hand line. Thererfore, a newcomer to spey could also be expected to learn how to spey cast with an appropriately sized mid-belly with its 65' belly spey line.
As can be seen by the above, I view the spey line standards as a good thing, just like the AFTMA single-hand line standards have been a good thing for the last 50 years in the single-hand fly world. As most or all of the line manufacturers produce lines conforming to the spey line standard that was adopted last fall, consumers will be able to buy any spey line of the same belly length with confidence that it will work on his rod. And as rod manufacturers begin getting 2-hand rods in the pipeline rated according to the spey line standard, a consumer will be able to know any rod rated for a 9 spey line will work with the same lines regardless of line manufacturer, just like it has worked in the songle-hand world for 40 years.
Right now we are in a transition phase of having the spey standard implememented, just like happened with single-hand rods. However, because of modern technology like the internet, this will happen much more quickly than the roughly 10 years it took from the late-50's when the AFTMA standards were adopted to the late-60's when virtually every rod maker and line maker were using them in the single-hand world. Does this mean there is a need for some experimentation to find out what new spey standard line wt works with a given rod? Of course, but just like with the single-hand world and its adopting the AFTMA single-hand line standards, experienced spey casters will have been experimenting to find out what spey lines work best with their favorite rods that were produced prior to rods being rated according to the spey line standard. Thus, shop owners, shop imployees, casting instrutors, and experienced spey casters will be able to provide the new or casual/occasional spey caster with the proper advise as to line size for his rod.