You have to keep in mind that (electric) guitar is still a relatively new instrument, especially on a virtuosic level. Instruments like violin and piano have been played brilliantly and at quick tempos for a long time now, whereas it wasn't until probably the latter half of the 20th century where guitarists really started (and there is still progression to this day) to figure out and master the instrument at a technical level. This is why with guitar it is difficult to simply pick up the instrument and practice 'til you get ''good.'' Correct practice is foreign to most guitarists these days, and you can practice all you want but until you practice correctly you will either not progress or you will be severely limited. This isn't as much a problem with other instruments where ''proper technique'' is a widely accepted/acknowledged thing, among teachers and books. You take a look at guitar though and there is just so much more that could go wrong with your posture/fingering/picking/etc. that it's much more sensitive/complicated in that aspect.
That's a fairly good point. There are definitely a bunch of guitarists who try to take shortcuts by sounding good due to their equipment, simply because they have the option to, and people in general like to take the easy way out. The natural showiness of guitar in general definitely contributes to the overuse of effects, however this doesn't make the mastery of the instrument any simpler. In the same way that vibrato and bow attack produce expression and articulation on the violin, guitarists must also use vibrato, pick attack/angling, muting, among many other factors, to produce a good sound. And honestly it's pretty easily recognizable when these basic things are not practiced in a guitarist's technique and he/she attempts to simply rely on effects.