There's a more likely explanation.
Netscape supports an extension to the <img> tag that looks like this:
<img src="big.gif" lowsrc="small.gif">
When the browser encounters a tag such as this, it loads and displays the
"lowsrc" image, and then gradually replaces the "lowsrc" with the "src"
image. That is the effect you were probably seeing. I've used this for
purposes other than resolution, such as displaying a picture and gradually
replacing it with a labelled version of the same picture.
[In a desperate attempt to avoid losing another mailing list to Netscape
I'm pretty fond of lowsrc as a bandwidth solution in gif display, since
I'm working for a high-end graphics house that doesn't like 16-bit
"trash" littering their pages. Might something of this nature work to
overcome bandwidth problems in vrml? For instance, deliver a "framework"
and then fill it in with textures?
[....well, I did say it was a _desperate_ attempt.]