Online inhibitions

What makes an online exhibition an exhibition? Is a digital catalogue an exhibition? A multimedia catalogue? What constitutes an exhibition?
Although my research to date has not been very exhaustive, I have come across quite a few web exhibitions so far. All present a combination of images, text and sometimes multimedia files or interactive games and the like, revolving around a given topic or collection of objects or artworks. So far so good. Too often, the graphic design and/ or the site navigation has been annoyingly clumsy, but enough webexhibition sites are both aesthetically pleasing and boast state of the art (animated) graphics and navigation. Which is great.
Still, I never quite get the feeling that I am experiencing an exhibition as such. Can’t quite put my finger on it, but it still seems more like a digital, hyperlinked and multimedial version of an exhibition catalogue, rather than a digital version of the exhibition itself.
So what makes an exhibition? What makes an exhibition experience? What makes a good exhibition experience? And is it at all possible to transfer this to the world wide web? Or is it the outing, the sociability, the architecture of the physical museum or perhaps the unique objects, complete with aura, that makes a visit to a physical exhibition a cultural experience?
Is it the fact that when visiting a physical exhibition, I make a concious decision to see this particular exhibition, allocate time for the visit, make my way to the museum, and once there I therefore actually go through the whole exhibition (if not the whole museum). I may not study every object in detail, I won’t be reading all the information available, but I will have made enough of an effort to create a lasting memory of my visit.
By contrast, the exhibitions that I find online, I stumble upon. I may be searching out webexhibitions, I may find one that interests or fascinates me, and yet, because of the habitual fast-scanning nature of webbrowsing, I rarely stick with the exhibitions long enough to properly engage. Whereas spending hours in a museums feels like a great pastime, I do not have the same patience with the online medium.
Is this just me, or is it a general problem? And if it is, is it the problem of the users, who must learn to slow down and engage with all the wonderful content avaiable online? Or is it the problem of the exhibition designers, who must find better ways to exhibit this content and help the audience engage?