My first guess is that it is a combination of Win7 and flash plugin. Why ? Meter speed shall be constant regardless of the hw platform, otherwise this game would make no sense (btw I am planning to record meter speed with various clubs to post them somewhere in the forums but I am still lacking time to do so). To achieve the meter has to be timer-driven, and the timer obviously is part of Flash API. The fact that it doesn't quite work with your laptop suggests that there is a miscalculation between the flash plugin and the API offered by Win7.
Few thing could be done to verify this: try to install WinXP on another partition on the laptop and check if the issue remains (or find a friend who's got the same or similar one with WinXP and will allow you to launch some practice shots).
Also, maybe it is worth checking if the flash version you've installed hasn't got mentioned somewhere in the release notes issues with Win7 platform (maybe there's even a separate Win7 release ? Is it a 64 or 32-bit system ?).
Second guess: I'm not sure if all laptops have that feature, but some have a utility to switch between different performance modes to balance consumption of battery power - you could check if your issue is not a result of having some kind of powersave or default mode turned on, which causes processor to reduce its frequency when the game is idle, but then when the meter is redrawn it wakes up to higher clock and it confuses the operating system and flash plugin timings driving meter speed.
Based on my experiences with laptops I considered them a poor choice for performance demanding tasks, and wgt is an example where stability of the environment is crucial for successful play. Your case seems to support that desktops are superior to laptops in that measure.