captainsolo said:

... LD is about 420i and VHS is about 240i IIRC. ...

Sounds like you are confusing video modes with analogue resolution.

Standard definition NTSC video is 480i - that includes VHS, LD and DVD. The video signal contains 480 horizontal lines of picture information (vertical resolution).

The ability of each of these lines to resolve fine detail is dependent on the analogue bandwidth - this can be measured in terms of horizontal resolution (vertical lines on the screen).

Roughly:
VHS = 3MHz, or 240 lines
Laserdisc = 5.5Mhz, 440 lines
DVD = 6.75MHz, 540 lines

You should never confuse this with digital resolution which is simply the number of discrete pixels, e.g. 720 x 480.