Kotari,
Thank you for taking the time to reply, but I am afraid that you didn't address my questions. What you said makes perfect sense to me if I were asking why textures/objects take longer in SL to load than in WoW, but that was not the question. The question is why the number of textures/objects would affect the way that they load--in other words, the problems with textures failing to rez completely, objects, especially sculpts, not rendering properly, avatars failing to load, etc. If all textures and all objects are rezzed by the same software (in a given viewer), the number of different textures and objects shouldn't make any difference except for the amount of time required to get the information (as you said).
You're welcome, I'm sorry I didn't do a very good job of explaining before though! Again, its a matter of things being saved to your computer versus being loaded via servers. In SL everything is stored via their servers, everything is using up your bandwith. However, if the files are stored in your computer then there is a lot of bandwith being freed up for other things like movement, gestures, scripts, ect. Its why things don't just load faster but are less likely to fail/glitch. In SL the reason things don't load sometimes is simply because your bandwith is struggling to do everything at once and then eventually it just gives up or thinks its loaded completely even when it hasn't.
I've used SL with cable internet as high as 50mbs but I've also used it with a connection as low as 4mbs. The difference in performance rises drastically the more bandwith you have to use. Essentially, lag is the root of all evil!
Note, that SL DOES have a place to store object/texture data (the cache) but its maxed out at 1gb versus the aforementioned 20+ for games like WoW. You can read more about that on the SL wiki under "cache".