For comparison:
US:
1995/09/09 PlayStation® introduced. (SRP 299 US Dollars)
1996/05/xx New price: PlayStation® (SRP 199 US Dollars)
1997/03/03 New price: PlayStation® (SRP 149 US Dollars)
1998/09/01 New price: PlayStation® (SRP 129 US Dollars)
1999/08/23 New price: PlayStation® (SRP 99 US Dollars)
2002/05/xx New price: PS one® (SRP 49 US Dollars)
2000/10/26 PlayStation®2 introduced. (SRP 299 US Dollars)
2002/05/xx New price: PlayStation®2 (SRP 199 US Dollars)
2003/08/xx New price: PlayStation®2 (SRP 179 US Dollars)
2004/05/xx New price: PlayStation®2 (SRP 149 US Dollars)
2006/04/20 New price: PlayStation®2. (SRP 129 US Dollars)
2006/11/17 PLAYSTATION®3 introduced. (HDD 60GB: SRP 599 US Dollars / HDD 20GB: SRP 499 US Dollars)
2007/07/09 New price: PLAYSTATION®3 (HDD60GB) (SRP 499 US Dollars)
2007/08/01 New PLAYSTATION®3 (HDD 80GB/including MotorStorm) introduced. (SRP 599 Dollars)
2007/10/18 New Price: PLAYSTATION®3 (HDD 80GB/including MotorStorm, SRP 499 US Dollars)
2007/11/02 PLAYSTATION®3 (HDD 40GB) introduced. (SRP 399 US Dollars)
JP:
1994/12/03 PlayStation® [SCPH-1000] introduced. (RRP 39,800 Yen)
1995/07/21 PlayStation®[SCPH-3000] eliminating S-video output introduced.(RRP 29,800 Yen)
1996/03/28 PlayStation® Fighting Box [SCPH-3500] introduced. (Including 2 controllers & 1 memory card / RRP 24,800 Yen)
1996/06/22 New price: PlayStation® [SCPH-5000] (Including 1 controller / RRP 19,800 Yen)
1997/11/13 PlayStation® with "SOUND SCOPE" [SCPH-7000] introduced. (Including 1 analog controller DUALSHOCK® /RRP 18,000 Yen)
1999/01/23 New price: PlayStation® [SCPH-7000/7500] (RRP 15,000 Yen)
2001/09/12 New price: PS one® [SCPH-100] (RRP 9,980 Yen)
2000/03/04 PlayStation®2 [SCPH-10000] introduced. (RRP 39,800 Yen)
2001/06/29 New price: PlayStation®2 [SCPH-30000] (RRP 35,000 Yen)
2001/11/29 New price: PlayStation®2 [SCPH-30000] (RRP 29,800 Yen)
2002/12/03 PlayStation®2 Ratchet & Clank Action Pack [SCPH-39000 RC] introduced. (RRP 26,800 Yen)
2003/02/13 PlayStation®2 Spring 2003 Color Model “SILVER” [SCPH-39000 S] introduced. (RRP 25,000 Yen)
2003/11/13 New price: PlayStation®2 [SCPH-50000 NB] (RRP 19,800 Yen)
2006/09/15 New price: PlayStation®2 [SCPH-77000] (RRP 16,000 Yen, including tax
2006/11/11 PLAYSTATION®3 intoduced. (HDD 60GB: Open price / HDD 20GB: RRP 49,980 Yen, including tax)
2007/10/17 New Price: PLAYSTATION®3 (HDD 60GB: RRP 54,980 Yen, including tax/ HDD 20GB: RRP 44,980 Yen, including tax
2007/11/11 PLAYSTATION®3 (HDD 40GB: RRP 39,980 Yen, including tax) DUALSHOCK®3 introduced.
SourcePS1 took 18 months to drop 50%
PS2 took 36 months to drop 50%
It's not so easy to compare PS3 as it had 2 SKUs, but it was available at launch for $500/¥50000. By the holidays this year PS3 will have been out 24 months, a $100/¥10000 cut will put it at a drop of 40% from launch compared to the 20Gb, or 50% compared to the 60Gb. The PS2 sold so well they could hold back on price drops, the same isn't true for the PS3, especially in Japan. A $100/¥10000 drop towards the end of the year would seem the most likely thing to happen, in my opinion.